BIOLOGY 

R 

G 


NEW-WORLD  SCIENCE  SERIES 

HUMAN 
PHYSIOLOGY 


AN   ELEMENTARY    TEXfT-$Op^ ^  f  ;; 
ANATOMY,   PHYSIOLOGY, 
AND   HYGIENE 


BY 


JOHN   W.    RITCHIE 

PROFESSOR   OF   BIOLOGY,    COLLEGE   OF   WILLIAM 
AND     MARY,   VIRGINIA 


Illustrated  by 
MARY  H.    WELLMAN 


imn     vUNIVEofRS1TY 


YONKERS-ON-HUDSON,  NEW   YORK 

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PREFACE 

FROM  a  considerable  experience  with  both  very  elementary 
and  more  advanced  classes,  the  author  has  been  led  to  certain  con- 
clusions in  regard  to  the  teaching  of  elementary  physiology  and 
hygiene.  It  is  not  proposed  to  enter  here  into  a  discussion  of 
the  correctness  of  these  conclusions,  but  a  brief  statement  of  a 
few  principles  that  seem  fundamental  may  perhaps  be  allowable. 

The  chief  object  of  teaching  physiology  in  the  public  schools 
is  to  train  the  pupils  to  keep  their  bodies  in  health.  The  mere 
teaching  of  anatomy  and  physiology  will  not  accomplish  this,  for 
the  pupil  cannot  master  the  structure  and  workings  of  the  body 
in  a  way  that  will  enable  him  to  frame  the  laws  of  health  and 
apply  them.  Neither  can  the  desired  end  be  reached  by  teach- 
ing rules  of  health  without  an  anatomical  and  physiological 
basis ;  for  without  such  a  basis,  hygiene  is  an  intangible  and  an 
elusive  subject.  The  author  has  therefore  concluded  that  a 
conservative  middle  course  is  wiser  than  either  of  the  extremes 
of  method  mentioned  above.  An  elementary  text  in  physiology 
should  be  a  balanced  text,  containing  sufficient  anatomy  to  make 
clear  the  broader  outlines  of  the  structure  of  the  human  body, 
enough  physiology  to  make  plain  the  great  laws  according  to 
which  the  body  lives,  and  a  full  discussion  of  how  a  violation  of 
these  laws  may  be  avoided. 

For  the  introduction  of  certain  new  matter,  as,  for  example, 
the  cell  idea,  the  work  of  enzymes,  and  matter  relating  to  germ 
diseases,  there  is  little  need  for  explanation.  The  groundwork 
of  physiology  and  pathology  has  in  recent  years  so  shifted  and 
extended  itself,  that  the  subject-matter  of  an  elementary  course 
must  to  a  considerable  extent  be  altered  if  it  is  to  furnish  a 


191222 


iv  PREFACE 

proper  basis  for  hygiene.  The  importance  of  teaching  the 
known  facts  in  regard  to  parasitic  diseases  and  of  training 
American  citizens  to  apply  measures  for  the  prevention  of  these 
diseases,  is  now  recognized,  and  the  reason  for  the  rather  full 
treatment  of  communicable  diseases  will  be  understood. 

One  other  point  in  connection  with  the  teaching  of  physiology 
has  constantly  obtruded  itself  upon  the  writer.  This  is  the  age 
of  science,  but  instead  of  teaching  elementary  science  in  our 
public  schools,  we  are  teaching  unrelated  fragments  from  differ- 
ent parts  of  the  field  of  science.  Physiology  more  than  any 
other  subject  is  the  people's  science,  and  it  should  be  related  to 
the  nature  study  and  the  agriculture  of  the  public  school  course. 
In  a  few  places  in  this  book  an  attempt  has  been  made  to  lead 
the  pupil  into  some  of  the  byways  that  connect  his  physiology 
and  nature  study,  and  special  emphasis  has  been  given  to  cer- 
tain facts  that  are  necessary  to  an  understanding  not  only  of 
physiology,  but  of  other  subjects  in  the  public  school  curriculum. 

For  counsel  and  very  great  assistance  during  the  preparation 
of  this  text,  the  author  must  thank  his  friend,  Professor  J.  S. 
Caldwell  of  Peabody  College  for  Teachers.  He  is  also  under 
obligation  to  Mr.  J.  C.  Freeman,  who  made  the  calculations  for 
the  table  on  pages  350-351 ;  and  for  many  suggestions  and  cor- 
rections he  is  indebted  to  the  following  persons:  Dr.  William  H. 
Park,  Research  Laboratory  of  New  York  City ;  Dr.  F.  H.  Pike, 
University  of  Chicago ;  Dr.  O.  P.  Jenkins,  Stanford  Univer- 
sity ;  Dr.  C.  M.  Hazen,  Medical  College  of  Virginia ;  Dr.  E.  G. 
Williams,  Virginia  State  Board  of  Health;  Dr.  S.  O.  Mast, 
Johns  Hopkins  University ;  Dr.  J.  A.  C.  Chandler,  Virginia 
Journal  of  Education ;  Professor  C.  W.  Hetherington,  Univer- 
sity of  Missouri ;  Miss  Virginia  Jones,  Williamsburg,  Virginia, 
Public  Schools  ;  Edward  Hughes,  Stockton,  California,  Public 
Schools;  and  W.  I.  Chapman,  Natick,  Massachusetts,  Public 
Schools. 


CONTENTS 

PAGE 

INTRODUCTORY    .  i 

CHAPTER 

I.    THE  HUMAN  BODY  A  COLONY  OF  CELLS  .        .        .        3 

II.    THE  PLAN  OF  THE  HUMAN  BODY    .  '.      16 

III.  THE  RULER  OF  THE  BODY        .  .      23 

IV.  THE  SKELETON          .        .  31 
V.     THE  SKELETON  (continued}      ...  .        -      45 

VI.     THE  MUSCLES    .        .        .'        .  59 

VII.     FOODS  AND  ENERGY          .  '7% 

VIII.     THE  DIGESTIVE  ORGANS  .... 

IX.     DIGESTION,  ABSORPTION,  AND  OXIDATION  OF  FOODS         .     110 

X.     DIETETICS          ....  .120 

XI.     THE  CIRCULATORY  SYSTEM       .        .  .     135 

XII.     RESPIRATION      .        .        .        .        .  •     160 

XIII.  VENTILATION     ....  .178 

XIV.  THE  KIDNEYS  AND  THE  BODY  WASTES   .  .  .     .     186 
XV.     THE  SKIN  AND  THE  BODY  HEAT     .  •  ,       •     19* 

XVI.     THE  NERVOUS  SYSTEM     .        ..        ...  •     210 

XVII.     THE  NERVOUS  SYSTEM  (continued}  .     •   *  •     225 
XVIII.     THE  EFFECTS  OF  ALCOHOL  ON  THE  HUMAN  BODY          .     238 


vi  CONTENTS 

CHAPTER  PAGE 

XIX.  THE  SPECIAL  SENSES        .        .        ...  .  -245 

XX.  THE  SPECIAL  SENSES  (continued}    .        .         .  .  .     259 

XXI.  ACCIDENTS         .        .        .'       .        ,        .        .  .  .     274 

XXII.  DISEASE  GERMS        .        .        .      . ;.        .     ,   *  .  •     285 

XXIII.  DISEASES  CAUSED  BY  PROTOZOA      .  .  .  .     292 

XXIV.  DISEASES  CAUSED  BY  BACTERIA       .        .        .  •  .  .     303 
XXV.  PREVENTING  THE  SPREAD  OF  DISEASE  GERMS  .  .    320 

XXVI.  TUBERCULOSIS  .       .. .. ., .    ... 340 

APPENDIX      .,        .        «        .        .    <    .       •,        .        .  .  .     347 

GLOSSARY        i        .        .        .        .        •        .        »        .  .  -355 

INDEX  .        .        .        .        .        .     -  .  i    i..       >        »  .  -357 


INTRODUCTORY 

DID  you  ever  get  up  in  the  morning  and  find  that  all  the 
world  seemed  bright  ?  And  did  you  ever  get  up  on  another 
morning  and  find  that  all  the  world  was  dull  ?  Do  you 
remember  how  on  the  one  morning  you  sang  over  your  work 
and  ran  on  your  way  to  school  ?  And  how  on  the  other 
morning  you  blundered  and  fretted  over  j'our  work  ana  did 
not  care  to  play  ?  On  the  one  day  you  were  so  happy  that 
every  one  was  pleased  to  see  you.  ,  Oii:t!ie  pther,  cl^y^yoiv 
were  not  a  pleasant  companion  for  any  one.  On  the  one 
day  the  world  seemed  a  beautiful  place,  and  work  was  easy. 
On  the  other  day  all  the  world  was  dull,  and  every  task  was 
hard  and  disagreeable. 

Why  were  you  happy  and  joyous  one  morning  and  misera- 
ble and  unhappy  the  next  ?  Why  did  you  cheerfully  do  your 
work  one  day  and  hate  the  same  work  the  next  day  ?  Was 
it  money,  clothes,  or  education  that  made  you  happy  ?  Was 
it  a  lack  of  them  that  made  you  unhappy  ?  All  these  things 
are  important,  but  there  is  something  else  much  more  im- 
portant than  all  of  them,  —  something  that  causes  happiness  to 
bubble  up  within  you  no  matter  what  the  world  is  like ;  some- 
thing that  keeps  the  heart  beating  strong  with  hope,  and 
makes  you  laugh  at  hard  work  ;  something  without  which  all 
the  wealth  of  the  world  cannot  make  you  happy,  and  with 
which  any  sound-minded  person  can  lead  a  useful  and  a 


2  INTRODUCTORY 

successful   life.      This  something  that  can  so  change  all  the 
world  for  you  is  the  healtJi  of  your  oivn  body. 

We  cannot  always  be  in  perfect  health.  Sickness  is  bound 
to  come  to  us  all,  for  there  are  many  things  about  the  human 
body  that  we  do  not  understand,  and  it  has  many  ailments 
that  we  cannot  escape  or  cure.  It  is  possible,  however,  for 
us  to  learn  many  things  that  will  help  us  to  avoid  the  ill- 
health  that  is  so  common  in  the  world.  In  this  -book  we 
shall,  therefore,  study  the  human  body  and  how  to  keep  it  in 
health. 


OF  THE 

UNIVERSITY 

OF 


CHAPTER    I 


THE   HUMAN  BODY  A  COLONY  OF  CELLS 

WHEN  you  view  a  brick  house  from  a  distance  you  do  not 
see  the  bricks  of  which  the  house  is  built ;  but  if  you  look  at 
the  house  through  a  telescope  or  come  close  to  it,  you  see 
clearly  the  bricks  in  the  walls  of  the  house.  The  house  which 
from  a  distance  appears  to  be  one  object  is  seen  to  be  com- 


FlG.  i.  Cells.  A  is  a  single  cell  as  it  appears  under  the  microscope,  B  is  a  cell 
showing  that  it  has  length,  breadth,  and  thickness,  and  C  is  a  group  of  cells.  A  cell 
found  alone  usually  has  a  somewhat  spherical  shape,  as  shown  in  A.  When  cells  grow 
in  groups  they  press  against  each  other  and  usually  have  an  irregular  shape,  as  shown 
in  C. 

posed  of  a  great  number  of  smaller  objects  built  together  to 
form  one  whole. 

The  human  body  is  composed  of  many  small  parts  called 
cells.  When  we  look  at  the  body  we  cannot  see  the  cells; 
but  when  a  small  portion  of  flesh  or  skin  or  other  part  of  the 
body  is  examined  under  the  microscope,  the  little  parts  which 

3 


4  HUMAN  PHYSIOLOGY 

make  up  the  body  can  be  distinctly  seen.  As  the  walls  of  the 
house  are  built  of  bricks,  so  the  human  body  is  built  of  cells. 

The  Cell.  A  cell  is  a  small  portion  of  a  transparent, 
jelly-like  material  called  protoplasm}-  Usually  a  cell  has  a 
thin  wall  about  it,  so  that  it  is  like  a  little  sac  filled  with  a 
clear,  half -liquid  substance.  In  each  cell  is  a  nucleus,  which 
is  a  denser  portion  of  the  protoplasm.  Both  the  nucleus 
and  the  less  dense  material2  around  it  take  in  food  and 
grow  ;  both  of  them  are  alive.  Taken  together  they  are  the 
protoplasm,  the  living  substance  of  the  cell. 

Living  Things  Composed  of  Cells.  As  a  heap  of  sand  is 
composed  of  small  grains,  so  are  living  things  composed  of 
very  tiny  cells.3  Every  blade  of  grass,  every  weed,  every 
flower,  and  every  tree  is  made  of  cells.  Every  animal, 
whether  it  be  large  or  small,  whether  it  live  in  the  water,  on 
the  land,  or  in  the  air,  is  composed  of  cells.  Dead  materials, 
like  earth,  stones,  water,  and  air,  are  not  made  of  cells,  but 
there  is  nothing  living  that  is  not  composed  of  cells. 

How  Cells  are  Formed.  The  ancient  Egyptians  thought 
that  crocodiles  and  frogs  came  from  the  mud  of  the  river 
Nile,  and  a  great  Grecian  philosopher  believed  that  insects 
sprang  from  the  dew.  A  wise  old  German  once  told  the 
people  how  mice  could  be  created  from  wheat  and  stagnant 
water.  Two  hundred  years  ago,  it  was  commonly  believed 
that  maggots  came  from  meat  and  cheese,  and  that  worms, 
insects,  snails,  and  eels  came  out  of  decaying  matter  and 

1  In  the  back  of  the  book  the  pupil  will  find  a  glossary  that  gives  the  pronun- 
ciations and  meanings  of  many  of  the  more  difficult  words. 

2  The  lighter  portion  of  the  protoplasm  is  called  cytoplasm. 

8  A  few  cells,  for  example,  a  frog's  egg,  are  large  enough  to  be  seen  with  the 
naked  eye.  In  general,  however,  cells  are  very  small;  so  small  that  it  would 
require  twenty-five  hundred  cells  from  the  human  body  to  make  a  row  an  inch 
long. 


THE  HUMAN"  BODY  A   COLONY  OF  CELLS 


5 


mud.  Fifty  years  ago,  many  physicians  and  other  scientific 
men  believed  that  disease  germs  and  other  little  microbes 
were  formed  from  unclean  and  decaying  matter,  and  many 
persons  still  think  that  this  is  true. 

We  know  now  that  all  these  ideas  are  incorrect.  All  living 
things,  from  the  smallest  germ  to  the  greatest  whale,  are 
made  of  cells,  and  a  cell  can  come,  not  from  dead  matter, 
but  only  from  another  living  cell. 


FIG.  2.  Cell  division.  The  nucleus  of  the  cell  divides  and  part  goes  to  each  end 
of- the  cell.  A  wall  is  formed  across  the  cell,  dividing  it  into  two  parts,  each  of  which 
is  a  cell.  All  new  cells  are  formed  in  this  way. 

The  nucleus  of  a  cell  divides,  and  part  of  it  goes  to  each 
end  of  the  cell.  Then  a  wall  forms  across  the  cell,  and 
divides  it  into  two  parts.  Each  part  is  a  new  cell  with  its 
own  nucleus,  and  each  part  grows  as  large  as  the  parent 
cell.  All  new  cells  are  formed  in  this  way.  "  Every  cell 
comes  from  a  cell." 

One-Celled  and  Many-Celled  Animals.  In  a  drop  of  stag- 
nant water  many  hundreds  of  little  animals  may  sometimes 
be  found, —  animals  so  small  that  you  can  see  them  only 
with  a  microscope.  One  of  these  little  animals  has  only  one 
cell  in  its  body.  The  animal  is  a  single  cell  that  swims 
about  alone  and  lives  by  itself.  When  this  cell  divides,  the 
two  new  cells  separate,  and  each  one  forms  a  new  animal. 


6  HUMAN  PHYSIOLOGY 

The  bodies  of  all  the  larger  animals  (for  example,  the 
body  of  the  chick  in  an  egg)  begin  with  a  single  cell,  but 
when  this  cell  divides,  the  new  cells  do  not  separate,  like 
those  of  the  one-celled  animals.  The  cells  remain  together 
and  keep  on  dividing  and  dividing  until,  in  the  body  of  a 
large  animal,  like  a  man,  there  are  millions  and  millions  of 
cells,  —  more  than  you  could  count  in  many  years.  The 


FIG.  3.  A  one-celled  animal  dividing.  This  cell  swims  about  in  the  water  by 
means  of  small  hair-like  cilia  which  beat  the  water.  When  it  divides,  the  new  cells 
separate  instead  of  remaining  together  as  they  do  in  the  many-celled  animals. 

difference  between  the  little  one-celled  animals  and  the  larger 
many-celled  animals  is  therefore  this :  in  one-celled  animals, 
the  cells  separate  after  they  divide  and  each  cell  lives  alone. 
In  the  many-celled  animals,  the  cells  remain  together  after 
division,  and  live  in  a  great  colony. 

Your  body,  therefore,  is  a  great  colony  of  cells,  and  each 
cell  in  it  corresponds  to  an  entire  one-celled  animal.  You 
might  almost  think  of  yourself  as  made  up  of  a  great  com- 
munity of  little  animals,  yet  this  idea  would  not  be  wholly 
correct.  The  cells  of  our  bodies  have  learned  to  live  to- 
gether. They  would  die  if  separated,  and  it  takes  them  all 
to  make  one  complete  animal. 


THE  HUMAN  BODY  A    COLONY  OF  CELLS  7 

Different  Kinds  of  Cells  do  Different  Kinds  of  Work.     The 

single  cell  of  a  one-celled  animal  must  do  many  different 
kinds  of  work  to  live.  It  has  no  hands  to  get  foo'd  for  it, 
no  teeth  to  chew  the  food,  and  no  stomach  to  digest  it.  It 
has  no  lungs  to  breathe  in  oxygen,  and  no  kidneys  to  throw 
off  its  poisonous  wastes.  It  lives  all  alone,  with  no  other 
cells  to  help  it,  and  it  must  do  everything  for  itself.  Each 
cell  in  the  human  body  has  the  same  needs  as  the  little 
animal  cell  which  lives  alone.  Each  must  have  food,  must 
get  oxygen  from  the  air,  and  must  get  rid  of  its  poison- 
ous wastes.  Many  of  our  cells  are  shut  up  in  the  center 
of  the  body,  where  they  can  get  neither  food  nor  oxygen  for 
themselves,  and  their  waste  matter  would  poison  both  them- 
selves and  their  neighbors  if  there  were  not  some  way  of 
getting  it  entirely  out  of  the  body.  Each  cell  cannot 
take  care  of  itself,  as  does  the  little  animal  in  the  drop  of 
water. 

You  can  easily  see  how  much  it  would  be  to  the  advantage 
of  all  the  cells  in  the  body  for  each  one  to  give  up  trying 
to  do  everything  for  itself,  and  for  all  of  them  to  unite  and 
work  for  the  good  of  the  whole  community.  This  they  have 
done.  They  have  divided  the  work,  and 
each  cell  has  taken  for  its  own  some  special 
task.  The  cells  of  the  stomach  digest  the 
food  ;  the  bone  cells  build  up  a  strong  frame- 
work to  support  the  body  ;  the  muscle  cells 

,       ,      .  .        ..,  FIG.  4.    Cells  from 

move  the  body  ;  the  kidney  cells  throw  out  aglandof  the  stom. 
wastes  ;  the  lung  cells  take  in  oxygen  from  ach.  The  function 


the  air  ;  and  the  cells  of  the  blood  (red  blood     fworkj 

is  to  digest  the  food. 

corpuscles)   carry  oxygen   through    all   the 

body  to   the  cells.       Each  cell  is  a  skilled  workman   doing 

some  particular   work    for   the   body   as   a  whole,  and   not 


A  •  » 

Connective  tissue.  In  its  first  stage 
connective  tissue  is  a  group  of  cells 
which  build  around  themselves  a  mass 
of  jelly-like  material,  as  shown  in  A. 
This  material  hardens  into  the  fibers 
that  are  seen  between  the  cells  in  D. 
All  through  the  body  a  framework  of 
connective  tissue  runs,  holding  the  cells, 
organs,  and  tissues  in  place. 


One  of  the 
nerve  cells 
from  the 
brain.  These 
cells  are  asso- 
ciated with 
thought. 


Cells  of  the  outer 
layer  of  the  skin. 
These  cells  form  a 
protective  covering 
for  the  body.  The 
outer  cells  die  and 
dry  up  until  they  are 
mere  scales. 


A  muscle  cell  from  the  stomach.  The 
muscle  cells  have  the  work  of  moving  the 
body. 


Bone  cells.  These  much-branched  cells 
deposit  around  themselves  bone  material 
(b),  thus  building  bones  to  support  the  body. 
The  bone  cells  build  a  network  of  fibers  like 
dense  connective  tissue  and  then  fill  the 
spaces  between  the  fibers  with  hard  mineral 
matter.  a  is  a  cavity  from  which  the  bone 
cell  has  been  removed. 


Fat  cells.  Food  for  the  body  is  stored  in 
these  cells.  Large  quantities  of  fat  collect 
in  the  cell,  and  crowd  the  protoplasm  (a 
and  b}  to  one  side.  A  fat  cell  is  little 
more  than  a  bag  of  oil. 


FIG.  5.    Cells  from  the  human  body.    Each  kind  of  cell  in  the  body  has  a 
particular  work  to  do  for  the  body  as  a  whole. 


8 


THE  HUMAN  BODY  A    COLONY  OF  CELLS 


an  unskilled  laborer  trying  to  do  all  the  many  different  kinds 
of  work  necessary  to  provide  for  its  own  wants. 

The  Cells  Dependent  on  Each  Other.  You  will  now  under- 
stand that  the  cells  in  the  body  must  depend  on  each  other  for 
many  things.  If  the  stomach  fails  to  digest  the  food,  there 
will  be  a  lack  of  food  in  all  the  cells.  If  the  kidneys  do  not 
throw  off  the  wastes,  all  the  cells  will  be  poisoned.  If  the 
lungs  stop  taking  in  oxygen,  all  the  cells  must  die  for  lack 
of  oxygen.  If  part  of  the  cells  fail  in  their  work,  all  the 
cells  must  suffer,  and  death  usually  comes  to  the  body  because 
part  of  the  cells  have  ceased  to  work. 

The  Body  compared  to  a  Community.  The  resemblance 
between  the  body  and  a  community  of  people  must  now 
be  very  clear  to  you.  In  both  the  body  and  the  com- 
munity we  have  individuals,  each  leading  his  own  life  and 
yet  making  a  part  of  a  greater  whole.  In 
the  community  we  have  individuals  of  dif- 
ferent occupations,  —  doctors,  teachers,  car- 
penters, blacksmiths,  grocers,  and  milkmen. 
In  the  body  we  have,  as  we  have  seen,  cells 
of  different  kinds, — muscle  cells,  bone  cells, 
digestive  cells,  and  many  others.  In  both 
the  body  and  the  community  the  individual 
does  not  provide  everything  that  he  uses, 
but  depends  on  others  for  many  things. 
The  carpenter  builds  houses  for  the  milk- 
man and  the  grocer,  and  these  persons 
bring  the  carpenter  his  food.  The  stom- 
ach cells  digest  food  for  the  cells  of  the 
lungs,  and  the  lung  cells  take  in  oxygen 
for  the  stomach  cells. 

Communities  are  prosperous  and  the  body  is  healthy  only 


FIG.  6.  Cells  from 
the  lining  of  the  tra- 
chea, a  is  a  cell  that 
manufactures  sticky 
mucus  (b)  in  which  dust 
and  germs  from  the  air 
are  caught.  The  cilia 
(c)  on  the  other  cells 
beat  upward  and  sweep 
the  mucus,  dust,  and 
germs  up  out  of  the 
air  passages  and  lungs. 


10  HUMAN  PHYSIOLOGY 

when  the  individuals  do  their  work  faithfully  and  well ;   for 

no  person  in  a  community  lives  to 
himself,  and  no  cell  in  the  body  lives 
to  itself,  but  each  has  a  share  in  the 
life  of  all.  New  individuals  from  time 
to  time  are  born  into  the  community 

FIG.  7.  Cells  from  the  blood.  and  other  individuals  die>  New  cdls 
A  is  a  white  corpuscle  whose 

function  is  to  kill  disease  germs;  are  constantly  being  formed  in  the 
B  is  an  edge  view  and  cis  a  side  body,  and  every  day  millions  of  cells 

view  of  the  red  corpuscles  that  ^.         ,       ,  .  _ 

carry  oxygen  through  the  body.       m     the     b°dy     are     destroyed.        Com- 

munities   increase  in  size  when  the 

number  of  births  in  them  exceeds  the  number  of  deaths,  and 
the  body  grows  when  the  number  of  new  cells  formed  in  it  is 
greater  than  is  the  number  of  the  cells  that  die.  Thus  in 
many  ways  the  body  resembles  a  community  of  people  where 
each  individual  is  doing  something  for  the  good  of  all. 

Tissues.  If  you  have  now  in  mind  what  has  been  said 
about  cells  and  their  work,  you  will  have  no  difficulty  in 
understanding  what  is  meant  by  tissties.  In  a  factory  we 
usually  find  the  workmen  who  do  the  same  kind  of  work  all 
collected  in  one  part  of  the  factory.  So  in  the  body  we 
usually  find  grouped  together  the  cells  which  do  the  same 
kind  of  work.  The  great  group  of  nerve  cells  is  in  the  brain. 
The  muscle  cells  are  collected  in  the  muscles,  and  the  kidney 
cells  in  the  kidneys.  Where  cells  of  one  kind  are  grouped, 
a  tissue  is  formed,  so  we  may  say  that  a  tissue  is  a  group  of 
cells  which  do  the  same  kind  of  work.  Muscle  tissue  is 
made  of  muscle  cells,  fatty  tissue  of  fat  cells,  and  nerve 
tissue  of  nerve  cells.  Each  tissue  is  a  group  of  cells  which 
do  some  particular  work  for  the  body  as  a  whole,  and  in 
return  have  many  things  done  for  them  by  the  cells  of  other 
tissues. 


THE  HUMAN  BODY  A    COLONY  OF  CELLS  \\ 

Organs.  An  organ  is  a  part  of  the  body  that  does  a  special 
work.  The  kidney  is  an  organ  for  throwing  out  wastes,  the 
lungs  are  organs  for  taking  in  oxygen,  the  eye  is  an  organ 
for  seeing,  and  the  stomach  is  an  organ  for  storing  and  digest- 
ing food.  Some  organs,  like  the  liver,  the  kidneys,  and  the 
heart,  are  chiefly  of  one  kind  of  tissue.  Other  organs  have 
in  them  many  kinds  of  tissues.  The  hand  is  an  example 
of  an  organ  of  this  kind,  bone,  connective  tissue,  muscle,  and 
skin  all  being  united  in  it  to  form  an  organ  for  grasping. 

Why  you  should  understand  the  Cell.  It  is  very  impor- 
tant for  you  to  understand  the  cell,  because  a  clear  idea  of 
the  cell  will  give  yon  a  new  way  of  thinking  about  all 
living  things.  Having  an  understanding  of  it,  you  will 
not  only  think  of  an  animal  as  a  living  thing,  but  you  will 
also  think  of  the  millions  of  cells  in  its  body,  each  filled 
with  living  protoplasm.  When  you  see  a  plant  cut  down, 
or  an  insect,  or  a  frog,  or  a  bird  killed,  you  will  not  only 
think  of  how  the  plant  or  animal  dies,  but  you  will  think 
of  how  all  the  little  cells  in  its  body  also  die ;  and  from 
thinking  of  the  living  objects  about  you  in  this  new  way, 
you  will  become  interested  in  many  things  which  you  do  not 
now  notice,  and  will  understand  much  that  now  seems  strange 
to  you.  When  you  see  a  rose  living  for  several  days  after  it 
has  been  cut  from  the  bush  and  placed  in  water,  or  when 
you  see  a  branch  of  a  plant  living  and  growing  when  placed 
in  the  soil,  you  will  know  that  when  a  part  of  a  plant  is  cut 
off  from  the  body  of  the  plant,  its  cells  need  not  always 
die.  If  you  read  that  when  a  starfish,  or  certain  kinds  of 
worms,  are  cut  into  pieces,  each  piece  grows  into  a  complete 
animal,  you  will  see  that  in  these  animals,  as  in  plants, 
the  cells  are  more  independent  than  in  the  human  body, 
and  that  a  group  of  them  is  able  to  live  without  the  rest  of 


12  HUMAN  PHYSIOLOGY 

the  body.  Also,  when  you  learn  to  think  of  animals  as  groups 
of  cells,  you  will  not  wonder  that  a  frog's  legs  should  twitch 
and  jerk  in  the  skillet;  or  that  after  the  head  has  been  cut 
off,  a  snake's  tail  can  live  and  move,  and  a  turtle  can  walk 
about.  For  you  will  understand  that  in  these  animals,  as 
in  the  rose,  part  of  the  cells  can  live  for  a  time  without  the 
others,  and  that  the  muscle  cells  are  living  and  moving  after 
the  brain  cells  are  dead.  All  these  things  and  many  others 
you  can  clear  up  for  yourself,  if  you  will  think  about  the 
cell  instead  of  about  the  body  as  a  whole. 

A  second  very  important  reason  why  you  should  under- 
stand the  cell  is  that  you  may  intelligently  care  for  your  ozvn 
bodies.  Each  of  the  great  multitude  of  cells  in  your  body  is 
following  out  its  own  little  life,  and  each  is  industriously  work- 
ing for  the  good  of  the  community  in  which  it  lives.  We 
hope  that  you  will  understand  that  your  cells  must  have 
proper  food,  oxygen,  exercise,  and  rest,  and  that  they  must 
get  rid  of  their  waste  matter.  You  should  realize  that  any 
medicine  you  take  can  act  on  the  body  only  by  being  carried 
by  the  blood  through  the  body  and  entering  the  living  proto- 
plasm of  the  cells.  If  it  helps  the  cells,  it  is  beneficial  to  the 
body,  and  if  it  injures  the  cells,  it  injures  the  body.  You 
should  understand  how  reckless  it  is  to  take  in  among  all  these 
delicate  cells  patent  medicines,  headache  remedies,  alcohol,  or 
tobacco,  unless  you  are  perfectly  certain  that  these  things  will 
not  harm  the  cells.  For  the  cells  of  your  body  are  the  most 
important  things  in  all  the  world  to  you.  If  they  become 
diseased,  you  will  fall  sick  ;  and  if  they  fail  in  their  work,  your 
life  must  cease.  When  the  bricks  crumble,  the  house  falls ; 
and  when  the  cells  are  dead,  the  body  is  dead,  for  the  life  is 
in  the  cell. 

There  is  a  third  'reason  why  you  should  understand  the 


THE  HUMAN  BODY  A    COLONY  OF  CELLS  13 

cell,  and  that  is  because  in  physiology  we  constantly  study  the 
work  of  the  different  kinds  of  cells.  If  you  did  not  under- 
stand the  figures  I,  2,  3,  and  4,  you  would  get  very  little 
pleasure  or  profit  from  trying  to  solve  problems  in  arith- 
metic; and  if  you  do  not  understand  what  a  cell  is  and 
how  the  body  is  made  up  of  cells,  you  will  think  that  physi- 
ology is  a  dull  subject  indeed,  and  it  will  never  mean  much  to 
you.  But  understanding  the  cell,  you  can  study  the  differ- 
ent parts  of  the  body  intelligently,  and  in  all  the  world  you 
will  find  nothing  more  wonderful  or  interesting  than  your 
own  body. 

Anatomy,  Physiology,  and  Hygiene.  Anatomy  is  the  study 
of  tJie  structure  of  the  body,  —  the  study  of  the  way  all  its 
organs  are  composed  of  tissues  and  its  tissues  made  of  cells, 
and  of  how  all  the  organs  and  tissues  are  joined  together  to 
make  one  body.  Physiology  is  the  study  of  the  function  of 
the  different  cells,  tissues,  and  organs,  —  the  study  of  the  work 
which  all  the  different  parts  of  the  body  do.  Hygiene  is  the 
study  of  how  to  keep  the  body  in  health.  These  three  subjects 
we  must  study  in  this  book. 

Summary.  The  human  body,  like  all  other  living  things, 
is  composed  of  cells.  Each  cell  is  a  little  piece  of  protoplasm 
that  takes  in  food  and  grows  and  is  alive.  Cells  are  formed 
only  by  the  division  of  other  cells,  and  living  things  can  come 
only  from  other  living  things  of  the  same  kind.  They  can- 
not come  from  dead  matter,  although  this  has  often  been 
believed. 

When  a  one-celled  animal  divides,  the  new  cells  separate. 
In  many-celled  animals  the  cells  remain  together  after  divi- 
sion, and  the  bodies  of  the  larger  animals  are  great  colonies 
of  cells.  Each  cell  of  the  human  body  corresponds  to  an 
entire  one-celled  animal.  Each  cell  in  the  body,  like  a  one- 


14  HUMAN  PHYSIOLOGY 

celled  animal,  must  have  food  and  oxygen  and  must  get  rid 
of  its  wastes. 

It  would  not  be  possible  for  a  cell  in  the  body  to  supply 
all  of  its  own  wants,  so  each  cell  spends  all  its  time  in  one 
kind  of  work,  and  depends  on  other  cells  for  many  things 
that  are  necessary  to  its  life.  It  follows,  therefore,  that  when 
part  of  the  cells  in  the  body  fail  in  their  work  the  whole  body 
must  die.  The  division  of  labor  among  the  cells  causes  the 
body  in  a  striking  way  to  resemble  a  community  where  the 
people  have  different  occupations  and  each  one  has  many  of 
his  wants  supplied  by  others. 

As  the  workmen  who  do  the  same  kind  of  work  in  a  fac- 
tory are  often  found  together,  so  the  cells  that  do  the  same 
kind  of  work  in  the  body  are  found  in  groups.  Such  a  group 
of  cells  —  cells  that  do  the  same  kind  of  work  —  is  called  a 
tissue.  An  organ  is  a  part  of  the  body  that,  like  the  hand  or 
the  eye,  is  fitted  for  some  special  work.  It  may  be  composed 
chiefly  of  one  or  of  many  kinds  of  tissues. 

A  clear  idea  of  the  cell  is  a  very  great  help  in  understand- 
ing all  living  things,  in  caring  for  our  own  bodies,  and  in  the 
study  of  physiology.  Anatomy  is  the  study  of  the  structure 
of  the  body,  Physiology  is  the  study  of  the  function  of  the 
different  organs  of  the  body,  and  Hygiene  is  the  study  of 
how  to  keep  the  body  in  health. 


QUESTIONS 

Of  what  is  the  human  body  composed  ?  Describe  or  draw  a  cell. 
What  kind  of  objects  are  composed  of  cells?  How  are  new  cells 
formed?  Where  do  living  things  come  from?  Give  some  of  the 
beliefs  that  have  been  held  by  different  people  in  regard  to  the  ori- 
gin of  animals  and  plants.  Describe  the  process  of  cell  division. 


THE  HUMAN  BODY  A    COLONY  OF  CELLS  15 

In  a  one-celled  animal  what  do  the  cells  do  after  division?  What 
do  the  cells  do  after  division  in  a  many-celled  animal  ?  What  in  the 
human  body  corresponds  to  an  entire  one-celled  animal?  What  are 
some  of  the  needs  of  a  cell? 

Explain  why  a  cell  in  the  body  could  not  provide  for  all  its  own 
wants.  Name  some  of  the  different  kinds  of  cells  in  the  body  and 
explain  the  function  (work)  of  each.  What  happens  to  the  body  if 
part  of  the  cells  fail  in  their  work?  Give  examples  of  cells  that 
must  do  their  work  to  keep  the  body  alive.  Mention  some  ways  in 
which  the  body  corresponds  to  a  community  of  people. 

What  is  a  tissue?  Name  some  of  the  body  tissues.  What  is  an 
organ?  Name  some  organs  of  the  body  and  give  their  functions. 

Give  three  reasons  why  it  is  important  to  understand  the  cell. 

What  is  Anatomy?     Physiology?     Hygiene? 


If  a  cell  and  a  peach  were  compared,  what  part  of  the  cell  would 
correspond  to  the  seed  of  the  peach?  to  the  flesh  of  the  peach?  to 
the  skin  of  the  peach? 

In  an  egg  there  is  one  living  cell  lying  on  the  side  of  the  yolk. 
What  is  necessary  to  make  this  cell  grow  and  divide?  Of  what  use 
are  the  yolk  and  white  of  the  egg  to  the  cell  within  the  egg?  Into 
what  have  the  yolk  and  the  white  been  changed  by  the  time  the  egg 
hatches? 

Does  the  cell  in  a  duck's  egg  grow  into  a  duck  and  the  cell  in  a 
hen's  egg  into  a  chick  because  the  food  supply  in  the  eggs  is  different, 
or  because  the  living  cells  in  the  eggs  are  different?  Are  the  cells  of 
your  body  always  composed  of  the  same  materials,  no  matter  what 
kind  of  food  you  eat? 

Can  a  branch  be  transferred  from  one  tree  to  another  and  still 
live?  Can  a  piece  of  tissue  be  transferred  from  one  person  to  an- 
other? Ask  a  physician  if  cells  from  the  body  of  an  animal  can  be 
transplanted  to  the  human  body. 

What  happens  in  a  wound  when  it  heals?  Ask  a  physician  how 
the  cells  in  a  scar  differ  from  the  cells  in  other  parts  of  the  skin. 


CHAPTER    II 

THE  PLAN   OF  THE  HUMAN   BODY 

THE  human  body  is  com- 
posed of  a  head,  a  trunk,  and 
two  pairs  of  limbs.  It  is  sup- 
ported by  a  skeleton,  the  most 
important  part  of  which  is  the 
spinal  column,  or  backbone. 
In  the  head  are  eyes,  ears,  a 
nose,  and  a  mouth.  The  body 

THORACIC  CAVITY ^P^ES^BKl  nas  m  ^  two  cavities,  3.  dorsal 

or  back  cavity,  and  a  ventral 
or  front  cavity.  In  these  two 
cavities  are  found  most  of  the 
organs  of  the  body. 

The  Dorsal  Cavity.  In  the 
head  is  a  great  cavity,  and 
opening  out  of  this  cavity  at 
the  base  is  a  long  passage- 
way that  runs  through  the 
spinal  column  from  top  to 
bottom.  The  cavity  in  the 
FIG.  8.  The  cavities  of  the  body.  The  head  and  the  canal  in  the 

dorsal  cavity  is  in  the  head  and  the  spinal   backbone)  taken   together,  are 

column.    The  ventral  cavity  is  in  the  front 

of  the  trunk  and  is  divided  by  the  diaphragm   the    dorsal       Cavity.       In     this 

into  an  upper  and  a  lower  part.  cavity  lie  the  great  centers  of 

the  nervous  system,  the  brain  and  the  spinal  cord. 

1  The  name  dorsat  comes  from  dor' sum,  the  Latin  word  for  back.    In  the  lower 
animals  it  is  easy  to  see  that  the  cavity  in  the  head  and  the  canal  in  the  spinal 

16 


ABDOMINAL  CAVITY 


THE  PLAN  OF  THE  HUMAN  BODY 


The  Ventral  Cavity.  The  ven- 
tral cavity  is  a  great  hollow  in 
the  front  part  of  the  trunk. 
Stretched  across  it  is  a  thin 
sheet  of  muscle,  called  the  dia- 
pliragm,  which  divides  it  into  an 
upper  and  a  lower  part.  The 
upper  part  is  the  chest  or  thoracic  ESOPHAGUS 
cavity.  It  contains  the  heart 
and  lungs  and  many  of  the  great 
blood  vessels.  The  lower  part 
is  the  abdominal  cavity.  In  the 
left  side  of  this  cavity,  its  outer 
end  close  up  under  the  dia- 
phragm, lies  the  stomach.  On 
the  right  side  of  the  body  and 
partly  covering  the  stomach 
is  the  liver.  The  intestine  is 
very  long  and  is  coiled  again 
and  again  in  the  abdominal  cav- 
ity, filling  most  of  it.  Attached 
to  the  back  walls  of  the  cavity 
are  the  two  kidneys,  which 
take  waste  matter  out  of  the 
body.  At  the  left  end  of  the 
stomach  is  a  dark  red  organ  called  the  spleen.  Along  the 
lower  back  part  of  the  stomach  is  the  pancreas,  a  very  im- 
portant digestive  organ,  whose  work  we  must  take  up  in 
another  chapter. 

Man's  Place  in  the  Animal  Kingdom.     Man  has  a  spinal 

column  are  all  part  of  one  long  cavity  that  runs  along  the  back  of  the  body  and 
widens  out  at  the  head  end  to  make  room  for  the  brain. 


FIG.  9.   Section  of  the  body  show- 
ing.the  Positions  of  the  organs  in  the 

' 


18 


HUMAN  PHYSIOLOGY 


column,  and  therefore 
belongs  among  the  ver- 
tebrates^ or  backboned 
animals.  He  has  hair, 
and  when  young  lives 
on  milk,  and  therefore 
he  belongs  among  the 
mammals,  the  highest 
class  of  the  vertebrates. 
The  five  classes  of  ver- 
tebrates are  the  fishes, 
amphibians,  reptiles, 
birds,  and  mammals. 
By  studying  Figure  n, 
you  can  learn  some  of 
the  animals  that  belong 
in  each  class,  and  which 
animals  are  closely 
related  to  man. 

The  Bodies  of  Verte- 
brates Similar.     A  fish,  a  frog,  a  lizard,  a  bird,  and  a  cat  do 

1  The  vertebrates  differ  from  worms,  insects,  and  other  lower  animals  in  having 
backbones.  The  five  classes  of  vertebrates  have  the  following  distinguishing 
characteristics : 

Fishes  live  in  the  water  and  breathe  by  means  of  gills. 

Amphibians  have  sticky  skins,  and  both  lungs  and  gills.  Some  salamanders 
have  lungs  and  gills  at  the  'same  time  and  can  breathe  either  in  the  water  or  in 
the  air.  Other  salamanders  have  gills  at  one  time  and  lungs  at  another.  Frogs 
and  toads  have  gills  in  their  early  life  and  lungs  in  their  later  life. 

Reptiles  have  scaly  skins  and  breathe  by  means  of  lungs.  Like  the  fishes  and 
amphibians,  reptiles  are  cold  blooded. 

Birds  have  wings  and  a  body  covering  of  feathers. 

Mammals  have  the  body  partly  or  entirely  covered  with  hair  and  feed  their 
young  with  milk.  The  mammals  and  birds  are  warm  blooded. 


FIG.  10. 


The  organs  in  the  ventral  cavity,  seen 
from  the  front. 


FIG.  ii.     The  vertebrate  animals.      Man  stands  at  the  head  oi  the  mammals,  the 

highest  class  of  the  vertebrates. 

19 


20  HUMAN  PHYSIOLOGY 

not  seem  much  alike ;  and  because  man  walks  upright,  the 
human  body  seems  very  different  from  the  bodies  of  all  these 
animals.  Yet  man  and  all  other  vertebrate  animals  are  built 
on  the  same  general  plan. 

Like  man,  all  the  vertebrate  animals  have  a  head  and  trunk, 
with  eyes,  ears,  and  a  mouth  in  the  head.  All  of  them  have 
a  dorsal  and  a  ventral  cavity  in  the  body,  with  in  general  the 
same  organs  in  these  cavities  as  are  found  in  man.  All  have 
skeletons  resembling  the  human  skeleton,  not  only  in  the 
spinal  column,  but  also  in  many  other  parts,  as  we  shall  see 
later.  All  of  them  have  two  pairs  of  limbs  corresponding  to 
the  arms  and  the  legs  of  man.  In  a  fish,  the  limbs  are  the  two 
pairs  of  fins  found  on  the  sides  of  the  body.  In  the  seal 
and  the  whale,  they  are  paddles  for  swimming.  In  most 
other  animals,  they  are  the  fore  and  hind  legs,  but  in  bats 
and  birds  the  fore  limbs  are  wings,  and  in  man  they  are  arms. 
Most  snakes  have  lost  their  limbs,  but  in  some  of  the  great 
snakes  the  remains  of  little  legs  can  be  found,  and  in  other 
reptiles  the  limbs  are  well  developed. 

How  Man  differs  from  Other  Vertebrates.  The  brain  of 
man  is  better  developed  than  is  the  brain  of  any  other  animal, 
and  in  many  ways  the  human  body  differs  to  a  certain  extent 
from  the  bodies  of  other  vertebrates.  But  the  great  difference 
between  man's  body  and  the  bodies  of  other  animals  is  that 
man  is  built  to  walk  erect.  Instead  of  carrying  the  head 
in  front  of  the  body  and  walking  on  all  four  limbs  in  the 
position  that  a  fish  is  in  when  it  swims  or  a  cat  is  in  when  it 
walks,  the  human  body  stands  on  the  hind  limbs,  with  the  body 
erect  and  the  head  above  the  body.  When  the  body  stands 
upright  the  fore  limbs  do  not  touch  the  ground.  Therefore,  in 
man  the  fore  limbs  are  not  fitted  for  walking,  but  are  arms 
and  have  hands  for  grasping. 


THE  PLAN  OF  THE  HUMAN  BODY  21 

Summary.  The  human  body  is  composed  of  a  head,  a 
trunk,  and  two  pairs  of  limbs.  It  has  in  it  a  dorsal  and  a  ven- 
tral cavity.  The  dorsal  cavity  contains  the  brain  and  the 
spinal  cord ;  the  ventral  cavity  is  divided  by  the  diaphragm 
into  the  thoracic  cavity  and  the  abdominal  cavity.  The  tho- 
racic cavity  contains  the  heart,  the  lungs,  and  many  great 
blood  vessels.  The  abdominal  cavity  contains  the  stomach, 
intestine,  liver,  spleen,  pancreas,  and  kidneys. 

Animals  with  backbones  are  called  vertebrates.  Vertebrates 
are  divided  into  five  classes,  —  fishes,  amphibians,  reptiles, 
birds,  and  mammals.  Man  has  a  backbone,  and  is  a  verte- 
brate. He  has  hair,  and  when  young  lives  on  milk ;  he  is 
therefore  a  mammal. 

The  bodies  of  other  vertebrates  are  built  on  the  same  plan 
as  the  human  body.  Every  vertebrate  has  a  head,  trunk, 
eyes,  ears,  and  a  mouth.  In  the  body  are  a  dorsal  cavity  and 
a  ventral  cavity.  It  has  a  skeleton  with  a  backbone,  and  has 
two  pairs  of  limbs  corresponding  to  our  arms  and  legs. 

Man's  body  differs  from  other  vertebrate  bodies  chiefly  in 
that  it  stands  erect.  The  fore  limbs  do  not  touch  the  ground 
in  walking,  and  are  arms  with  hands. 


QUESTIONS 

Name  the  principal  divisions  of  the  human  body.  How  is  the 
body  supported  ?  What  two  cavities  are  in  the  body  ? 

Where  is  the  dorsal  cavity?  What  does  it  contain?  Into  what 
two  parts  is  the  ventral  cavity  divided  ?  What  is  the  partition  be- 
tween these  parts  called?  Name  the  organs  in  the  thoracic  cavity; 
in  the  abdominal  cavity.  Locate  the  stomach.  Locate  the  liver. 

Name  the  five  classes  of  vertebrates.  To  which  class  does  man 
belong?  How  does  this  class  differ  from  other  vertebrates? 


22  HUMAN  PHYSIOLOGY 

Give  four  ways  in  which  the  bodies  of  all  vertebrates  are  similar. 
Mention  some  different  kinds  of  vertebrate  limbs.  How  does  man 
differ  from  other  vertebrate  animals  ? 


What  animals  do  you  know  that  are  not  vertebrates?  Can  you 
name  an  animal  that  has  no  head  ?  one  with  no  mouth  ?  one  with  no 
eyes?  one  with  no  ears?  Name  some  animals  that  differ  from  verte- 
brates in  the  number  of  their  limbs. 

How  does  a  fish  differ  from  other  vertebrates?  What  is  the  dif- 
ference between  a  shark  and  a  true  fish  ?  How  does  an  amphibian 
differ  from  other  vertebrates?  a  reptile?  What  are  the  four  reptile 
groups?  What  do  you  know  about  the  reptiles  that  lived  in  former 
ages  of  the  world  ? 

Which  is  the  lowest  mammal  shown  in  Figure  1 1  ?  In  what  way 
is  this  mammal  like  birds  and  reptiles,  and  different  from  the  mam- 
mals of  other  groups?  How  do  marsupials  differ  from  other  mam- 
mals? In  what  country  is  the  sloth  found?  Name  some  mammals 
that  live  in  the  water.  Do  these  mammals  have  lungs  or  gills?  On 
what  do  the  ungulates  (hoofed  animals)  feed?  On  what  do  the 
carnivora  feed?  the  primates? 

Can  you  name  some  relative  of  the  seal?  Where  do  most  of  the 
weasel  family  live  and  what  is  obtained  from  this  group  of  animals? 
Name  some  members  of  the  cat  family  not  shown  in  Figure  n  ;  of 
the  dog  family.  What  small  North  American  animal  is  closely 
related  to  the  bears?  Name  some  rodents  (gnawers)  that  are  larger 
than  any  of  the  rodents  shown  in  Figure  n.  Draw  in  a  larger  form 
the  ungulate  branch  of  the  vertebrate  tree,  putting  on  it  all  the 
hoofed  animals  that  you  know.  Do  you  know  any  families  of  mam- 
mals not  shown  in  Figure  r  i  ? 


CHAPTER    III 

THE  RULER  OF  THE  BODY 

ALL  parts  of  the  body  must  be  controlled  and  made  to 
work  together.  Over  them  all  a  ruler  must  be  set.  Not 
only  must  the  different  organs  be  kept  at  work,  but  each 
must  be  made  to  do  the  proper  amount  of  work,  and  to  do 
it  at  the  right  time.  If  the  digestive  organs  should  begin 
to  work  when  nothing  had  been  eaten,  their  work  would 
be  useless.  If  the  sweat  glands  should  begin  to  pour  out 
sweat  on  the  skin  when  the  body  was  not  hot,  their  work 
would  be  not  only  useless,  but  even  harmful.  If  all  the 
muscles  should  begin  to  pull  and  jerk  without  any  order 
or  system  (as  they  do  in  convulsions),  they  would  succeed 
only  in  throwing  the  body  to  the  ground. 

The  ruler  of  the  body  is  the  nervous  system.  When  we 
walk,  it  is  the  nervous  system  that  causes  the  right  muscles 
to  move.  When  we  eat,  the  nervous  system  sets  the  diges- 
tive organs  to  work.  It  keeps  the  heart  and  lungs  going, 
and  governs  all  the  body.  The  function  of  the  nervous  sys- 
tem is  to  govern  all  the  organs  of  the  body,  and  to  cause  them 
all  to  work  together  for  the  common  good. 

The  Divisions  of  the  Nervous  System.  The  nervous  sys- 
tem has  two  great  divisions,  —  the  central  nervous  system 
and  the  sympathetic  nervous  system.  The  great  centers  of 
the  central  nervous  system  are  the  brain  and  the  spinal 
cord.  The  central  nervous  system  controls  the  voluntary 

23 


NERVES 


FIG.  12.     The  nervous  system.     From  the  brain  and  spinal  cord,  nerves  run 

to  all  parts  of  the  body. 

24 


THE  RULER   OF  THE  BODY  2$ 

muscles  (those  which  we  can  move  when  we  wish),  and  its 
higher  centers  act  as  the  organ  of  tJie  mind. 

The  sympathetic  nervous  system  controls  the  glands1  of 
the  body  and  the  involuntary  muscles  (those  which  we  can- 
not control  by  the  will,  as  the  muscles  of  the  stomach,  intes- 
tine, heart,  and  blood  vessels). 

The  Brain  and  the  Spinal  Cord.  The  brain  has  three  divi- 
sions,—  the  cerebrum,  the  cerebellum,  and  the  medulla  oblon- 
gata.  The  spinal  cord  is  the  soft  white  substance  that  you 


MEDULLA  OBLONGATA 

FIG.  13.    The  brain. 

may  have  seen  in  the  backbone  of  an  animal.  In  the  back- 
bone of  a  man  it  is  a  little  thicker  than  a  lead  pencil.  At  the 
base  of  the  skull  is  a  great  opening,  through  which  the  spinal 
cord  enters  the  cranium  (page  34)  and  joins  the  brain. 

The  Membranes  of  the  Brain  and  Cord.  Around  the  brain 
and  cord  are  three  connective  tissue  membranes.  The 
outermost  membrane,  which  is  thick  and  tough,  is  called 

1The  salivary  glands,  glands  of  the  stomach  and  intestine,  the  pancreas,  liver, 
kidneys,  and  sweat  glands  are  some  of  the  glands  in  the  body. 


26 


HUMAN  PHYSIOLOGY 


the  dura  mater.  It  lines  the  entire  dorsal  cavity  of  the 
body,  both  the  cavity  of  the  cranium  and  the  cavity  in  the 
spinal  column.  The  innermost  membrane,  which  is  thin  and 
delicate,  is  called  the  pia  mater.  It  lies  close  to  the  surface 
of  the  cord  and  brain  and  dips  down  into  all  the  wrinkles 
and  folds  in  the  surface  of  the  brain.  In  it  are  the  blood 

vessels  that  nourish  the  outer  parts 
of  the  brain  and  cord.  Between 
the  dura  mater  and  the  pia  mater 
is  a  third  membrane,  the  aracJmoid 
membrane.  These  membranes * 
hold  the  very  soft  and  delicate 
brain  and  cord  in  place  and  keep 
them  from  being  shaken  about 
within  the  dorsal  cavity. 

The  Cerebro-spinal  Fluid.  The 
brain  and  spinal  cord  are  still 
further  protected  by  a  layer  of 
liquid  around  them  called  the  cere- 
The  base  of  the  skull,  bro-spinal  finid.  This  fluid  is  under 
the  arachnoid  membrane  —  that  is, 
between  the  arachnoid  membrane 
and  the  pia  mater  —  and  entirely 

surrounds  the  cord  and  brain.  It  acts  as  a  cushion  inside  the 
walls  of  the  dorsal  cavity  and  keeps  the  brain  and  cord  from 
striking  against  the  walls  of  the  cavity. 

Nerves.  From  the  under  surface  of  the  brain  and  from  the 
spinal  cord,  shining  white  nerves  pass  out  to  every  part  of 
the  body.  If  you  should  examine  one  of  these  nerves  under 

1  The  three  membranes  taken  together  are  called  the  meninges  of  the  brain 
and  cord.  Cerebro-spinal  meningitis  is  a  disease  caused  by  germs  growing  in 
these  membranes  and  in  the  cerebro-spinal  fluid. 


FIG.  14. 

showing  the  opening  through 
which  the  spinal  cord  enters  the 
cranium. 


THE  RULER   OF  THE  BODY  2/ 

a  microscope,  you  would  find  that  it  is  made  of  many  hun- 
dreds of  very  fine  fibers,  bound  together  by  connective  tissue. 
Although  these  fibers  are  so  slender  that  they  cannot  be  seen 
without  a  microscope,  some  of  them  are  of  great  length,  the 
longest  reaching  from  the  spinal  cord  to  the  hands  and  feet. 
In  the  larger  nerve  trunks  the  fibers  are  bound  up  in  a 
number  of  bundles,  which  are  all  wrapped  together  in  a  com- 
mon sheath  (Fig.  15).  The  larger  nerves  divide  into  smaller 


BLOOD  VESSELS 


FiG.  15.  A  is  a  cross-section  of  a  nerve,  showing  the  bundles  of  nerve  fibers  that 
make  up  the  nerve,  wrapped  in  the  connective  tissue  sheath.  B  is  one  of  the  bundles 
of  nerve  fibers  shown  in  A,  enlarged  to  show  the  individual  fibers. 

branches  containing  only  a  few  bundles,  or  sometimes  only 
one  bundle.  In  the  finest  nerve  branches,  the  bundles  of 
nerve  fibers  finally  break  up  into  the  separate  fibers,  many 
thousands  of  which  end  in  the  skin  and  muscles,  and  in  the 
other  organs  of  the  body. 

The  Function  of  Nerves.  The  function  of  the  nerves  is  to 
carry  messages  betiueen  the  different  parts  of  the  body  and  the 
brain  and  spinal  cord. 

Some  nerves  carry  messages  to  the  brain  and  cord.  By 
these  messages  we  learn  when  anything  touches  the  body, 


28  HUMAN  PHYSIOLOGY 

when  the  body  is  hungry  or  thirsty,  or  hot  or  cold,  when  it 
is  in  pain,  and  about  the  things  that  we  see,  hear,  taste,  and 
smell.  Other  nerves  carry  messages  outward  from  the  brain 
and  cord,  causing  the  muscles  to  move,  and  making  all  the 
parts  of  the  body  to  work  together  in  harmony.  The  power 
by  which  we  feel,  think,  and  will  lies  in  the  brain.  The 
commands  that  we  send  out,  causing  voluntary  movements 
of  the  muscles,  start  from  the  brain.  The  nerves  are  useful 
only  to  carry  to  the  cord  and  the  brain  messages  which  tell 
us  about  the  body  and  the  outside  world,  and  to  carry  com- 
mands outward  from  the  brain  and  cord  to  the  muscles  and 
to  the  other  organs  of  the  body. 

The  Telegrapher  and  the  Telegraph  Wires.  The  brain  and 
spinal  cord  are  often  compared  to  a  telegrapher  in  an  office, 
and  the  nerves  in  the  body  to  telegraph  wires  that  run  out 
in  all  directions  from  the  office.  Over  the  wires  the  tele- 
grapher receives  messages  that  tell  him  what  is  going  on 
about  him,  and  he  sends  out  messages  commanding  that  cer- 
tain things  be  done.  So  through  some  of  the  nerves  the 
brain  and  cord  receive  messages  which  tell  them  about  the 
body  and  the  things  going  on  around  it;  and  over  other 
nerves  they  send  messages  out  commanding  the  muscles  to 
move  the  body,  and  the  different  organs  to  do  their  work 
according  to  the  body's  needs. 

Necessity  for  a  Nervous  System.  From  this  you  will  under- 
stand that  the  nervous  system  connects  all  parts  of  the  body 
and  causes  all  the  organs  to  work  together  for  the  good  of 
the  body  as  a  whole.  Without  a  nervous  system,  the  human 
body  would  not  be  one  body  at  all,  but  a  mass  of  flesh  and 
blood  and  bones,  the  different  organs  working  not  at  all,  or 
working  without  plan  or  system,  and  the  whole  body  certain 
to  die  in  a  few  minutes.  With  a  nervous  system  it  is  the  living, 


THE  RULER   OF  THE  BODY  29 

moving,  speaking  human  body,  the  most  wonderful  thing 
in  all  the  world. 

Summary.  The  nervous  system  controls  all  parts  of  the 
body  and  causes  them  to  work  together.  The  great  divisions 
of  the  nervous  system  are  the  central  nervous  system  and  the 
sympathetic  nervous  system.  The  central  system  controls 
the  voluntary  muscles ;  its  chief  center  (the  brain)  is  the 
organ  of  the  mind.  The  sympathetic  system  controls  the 
involuntary  muscles  and  the  glands  of  the  body. 

The  brain  has  three  divisions  —  the  cerebrum,  the  cere- 
bellum, and  the  medulla  oblongata.  Around  the  brain  and 
cord,  and  protecting  them,  are  three  membranes  —  the  dura 
mater,  pia  mater,  and  arachnoid  membrane  —  and  a  layer  of 
cerebro-spinal  fluid. 

Nerves  are  composed  of  nerve  fibers.  Nerve  fibers  carry 
messages  between  the  different  parts  of  the  body  and  the  brain 
and  spinal  cord.  Some  fibers  take  messages  to  the  brain 
and  cord,  and  some  fibers  carry  messages  away  from  the 
brain  and  cord.  The  nerve  centers  (brain  and  cord)  may  be 
compared  to  a  telegrapher,  and  the  nerve  fibers  to  telegraph 
wires.  The  incoming  messages  bring  information  about  the 
body  and  the  world  around  the  body,  and  the  outgoing 
messages  are  commands  from  the  nerve  centers  to  the 
muscles,  glands,  and  other  organs. 

Without  a  nervous  system  the  different  organs  of  the 
human  body  would  work  without  system,  or  would  not  work 
at  all,  and  the  body  would  die.  By  the  nervous  system,  all 
the  body  parts  are  made  to  work  harmoniously  together,  — 
all  are  united  into  one  wonderful  body. 


30  HUMAN  PHYSIOLOGY 


QUESTIONS 

What  is  the  function  of  the  nervous  system?  Name  the  two 
divisions  of  the  nervous  system.  What  are  the  chief  centers  of  the 
central  nervous  system  ?  What  is  one  of  the  great  functions  of  this 
system?  With  what  part  of  the  nervous  system  is  the  mind  associ- 
ated? What  is  the  function  of  the  sympathetic  nervous  system? 

Name  the  three  divisions  of  the  brain.  Name  the  three  mem- 
branes that  are  around  the  spinal  cord  and  brain.  What  is  the 
function  of  these  membranes?  What  is  between  the  arachnoid  mem- 
brane and  the  pia  mater?  What  is  its  function? 

Describe  the  structure  of  a  nerve.  How  long  are  the  longest 
nerve  fibers  in  the  body?  What  is  the  function  of  a  nerve? 

In  comparing  the  nervous  system  to  a  telegrapher  and  a  tele- 
graph system,  what  part  of  the  nervous  system  corresponds  to  the 
telegrapher?  What  is  the  function  of  this  part  of  the  nervous 
system  ?  What  part  of  the  nervous  system  corresponds  to  the  tele- 
graph wires?  What  is  the  function  of  this  part  of  the  nervous 
system  ? 

To  what  part  of  the  body  are  the  incoming  messages  carried? 
What  is  the  effect  of  these  messages?  To  what  organs  are  the  out- 
going messages  taken?  What  is  the  effect  of  these  messages? 

Why  is  a  nervous  system  necessary  in  the  body? 


Why  is  it  possible  for  a  tree  to  live  without  a  nervous  system, 
when  a  man  cannot  do  so  ?  If  the  cells  in  the  human  brain  should 
become  cold,  would  they  die  ?  Do  the  cells  in  the  feet  or  ears  die 
if  they  become  cold  ?  If  a  fish  should  be  frozen  in  the  ice,  would 
the  cells  of  its  brain  be  killed?  Are  little  one-celled  animals  killed 
by  cold  water?  Ask  a  physician  which  cells  in  the  body  are  most 
affected  by  such  poisons  as  strychnin,  opium,  nicotine  (the  poison  in 
tobacco),  and  alcohol. 


CHAPTER  IV 

THE  SKELETON 

THE  skeleton  is  the  framework  on  which  the  body  is 
built.  The  shape  of  the  body,  therefore,  is  determined  prin- 
cipally by  the  skeleton.  Examine  your  own  body,  and  you 
will  readily  understand  that  this  is  true.  Feel  your  head, 
and  under  your  hair  and  skin  you  will  find  the  bones  which 
give  the  head  its  form.  In  the  fingers  and  toes  are  bones 
which  determine  whether  they  shall  be  long  and  slender,  or 
short  and  thick.  Down  the  middle  of  your  back  you  can 
feel  a  row  of  bones  u-nder  the  skin,  and  so  through  all  the 
body  you  will  find  bones  under  the  skin  and  muscles,  out- 
lining the  forms  of  the  different  parts. 

The  Functions  of  the  Skeleton.  The  first  function  of  the 
skeleton  is  to  support  the  body.  Without  a  skeleton,  the  body 
would  be  weak  and  soft,  and  the  head,  arms,  legs,  and  trunk 
would  fall  together  in  a  confused  mass.  But  the  bones 
are  hard  and  stiff,  and  form  a  strong  framework,  so  that 
each  part  of  the  body  stays  in  its  proper  place,  and  the  whole 
body  can  stand  upright. 

TJie  second  function  of  the  skeleton  is  to  protect  parts  of  the 
body  that  are  easily  injured.  The  bones  of  the  head  form 
a  strong  box  to  protect  the  brain ;  the  spinal  column  holds 
the  spinal  cord  safe  in  the  cavity  in  its  center;  and  the  bones 
of  the  chest  protect  the  heart  and  lungs. 


SPINAL  COLUMN 
CLAVICLE 


SCAPULA 


TARSAL  BONES 
ETATARSAL  BONES 
PHALANGES 


FIG.  16.    The  skeleton  of  the  human  body. 
32 


THE  SKELETON 


33 


The  third  function  of  the  skeleton  is  to  provide  a  system  of 
levers,  by  means  of  which  the  body  can  be  moved.  Moving  the 
body  is  the  special  function  of  the  muscles,  and  we  shall 
take  up  this  subject  in  the  next  chapter.  But  you  can  easily 
understand  that  without  a  skeleton  such  movements  as  walk- 
ing or  raising  the  arm  would  be  impossible. 

THE  PRINCIPAL   BONES   OF  THE   SKELETON 


FIG.  17.    The  skull. 

There  are  two  hundred  and  six:  bones  in  the  human  skeleton. 
They  are  divided  naturally  into  three  groups.  The  first  group 
contains  the  twenty-eight  bones  of  the  head,  the  second  group 
the  fifty-eight  bones  of  the  trunk,  and  the  third  group  the  one 
hundred  and  twenty  bones  of  the  limbs. 

The  Skull.  The  twenty-eight  bones  of  the  head  taken  to- 
gether compose  the  skull.  Eight  of  these  bones  are  solidly 


34 


HUMAN  PHYSIOLOGY 


united  to  form  a  box  (the  cranium)  for  the  protection  of  the 
brain.  Six  little  bones  are  in  the  ears  (Fig.  120),  and  the 
other  fourteen  bones  of  the  skull  form 
the  skeleton  of  the  face.  All  the  bones 
of  the  face  are  in  pairs  except  the  lower 
jawbone  and  the  thin  bone  which  forms  the 
partition  between  the  two  sides  of  the  nose. 
The  Spinal  Column.  The  spinal  column 
is  composed  of  twenty-four  vertebra  (sin- 
gular, vertebra),  the  sacrum,  and  the  coccyx. 
It  supports  the  parts  of  tJie  body  above  the 
hips,  and  protects  the  spinal  cord.  When 
it  is  broken,  standing  or  walking  is  im- 
possible, because  the  trunk  has  no  support, 
and  because  the  spinal  cord,  through  which 
the  muscles  that  keep  the  body  erect  are 
governed,  is  injured. 

To  do  its  work,  the  spinal  column  must 
have  strength  enough  to  carry  the  weight 
of  the  trunk,  head,  and  arms,  and  must 
bend  easily  in  all  directions,  yet  not  sharply 
enough  at  any  one  point  to  crush  the  deli- 
cate spinal  cord  within  it.  If  it  were  com- 
posed of  long  bones,  either  it  would  be  stiff 
and  allow  little  movement  of  the  upper 
parts  of  the  body,  or  it  would  bend  sharply 
at  the  joints  as  the  arms  do  at  the  elbows 
and  the  legs  at  the  knees,  and  injure  the 

FIG.IB.   Thrspinai  cord  at    these  Points-      But    because    the 

column.          spinal  column  is  composed  of  many  short 

bones,  and  has  many  joints,  it  allows  the  body  to  bend  freely 

forward  or  backward,  or  from  side  to  side,  yielding  a  little  at 


THE  SKELETON 


35 


each  joint,  but  not  enough  anywhere  to  crush  the  cord.  Also, 
because  the  spinal  column  is  flexible,  bending  at  so  many 
different  points,  it  rarely  happens  that  it  is  broken,  as  would 
be  the  case  if  the  trunk  were  carried  on  a  stiff  support. 


FLOATING  RIBS 


FIG.  19.    The  bones  of  the  trunk. 

The  Sternum  and  Ribs.  The  sternum,  or  breast  bone,  is 
a  flat  bone  lying  in  the  front  of  the  chest.  The  ribs  are 
long,  slender  bones,  which  curve  around  the  chest.  They  are 
twenty-four  in  number,  — twelve  pairs.  All  the  ribs  are  joined 


36  HUMAN  PHYSIOLOGY 

to  the  vertebrae  at  the  back.  The  seven  upper  pairs  are 
joined  to  the  sternum  in  front,  and  are  called  true  ribs. 
The  five  lower  pairs  of  ribs  are  called  the  false  ribs.  The 
three  upper  pairs  of  false  ribs  have  their  front  ends  attached 
to  the  lowest  pair  of  true  ribs.  The  two  lowest  pairs  of  false 
ribs  are  called  floating  ribs,  because  their  front  ends  are  free. 
The  ribs  protect  the  heart,  lungs,  stomach,  liver,  and  other 
organs  lying  in  the  upper  part  of  the  ventral  cavity,  and  form 
a  framework  to  which  the  muscles  that  are  used  in  breathing 
are  attached. 

The  Bones  of  the  Shoulder.  The  clavicle  (collar  bone) 
and  the  scapula  (shoulder  blade)  form  the  skeleton  of  the 
shoulder.  The  scapula  lies  in  the  back  of  the  shoulder.  In 
its  outer  end  is  a  socket  for  the  upper  end  of  the  arm  bone. 
The  weight  of  the  arm,  and  of  anything  which  is  lifted  by  the 
arm,  pulls  downward  on  the  scapula.  The  scapula,  therefore, 
has  powerful  ligaments  and  muscles  attaching  it  to  the  ribs 
and  to  the  vertebrae,  and  holding  it  in  place. 

The  inner  end  of  the  clavicle  is  joined  to  the  sternum,  and 
the  outer  end  is  propped  against  the  point  of  the  scapula, 
thus  bracing  the  shoulder.  When  the  clavicle  is  broken,  as 
often  happens  when  one  falls  on  the  shoulder,  the  point  of 
the  shoulder  drops  downward  and  forward.  By  feeling  your 
own  shoulder,  you  can  easily  locate  the  clavicle  running 
out  from  the  sternum  to  the  point  of  the  shoulder,  and  the 
scapula,  with  its  bony  ridge,  in  the  back  of  the  shoulder. 

The  Pelvic  Bones.  Place  your  hands  on  your  sides,  and 
you  will  feel  the  two  large,  irregular,  wide-spreading  pelvic 
bones.  They  are  firmly  joined  to  the  sacrum  behind  and  to 
each  other  in  front.  These  three  bones  with  the  coccyx  form 
\hepelvis,  which  balances  on  top  of  the  thigh  bones,  and  gives 
a  firm  support  for  the  upper  parts  of  the  body.  The  lower 


THE  SKELETON 


37 


abdominal  organs  lie  within  the  bowl-shaped  pelvis,  and  are 
partly  supported  by  it,  and  many  great  muscles  are  attached 
to  the  sacrum  and  to  the  pelvic  bones. 

The  Bones  of  the  Limbs.  Each  limb  has  in  it  thirty  bones, 
and  the  bones  of  the  arms  and  the  legs  are  very  similar  (Fig. 
33).  Each  has  a  large  bone  in  the  upper  part,  the  hunter  us 
in  the  arm,  and  the  femur  in  the  thigh.  Each  has  two  bones 
in  the  lower  part,  the  radius  and  the  ulna  in  the  forearm, 
and  the  tibia  and  fibula  in  the  leg  below  the  knee.  In  both 
the  wrists  and  the  ankles  we  find  a  group  of  small  bones,  the 
eight  carpal  bones  in  the  wrist,  and  the  seven  tarsal  bones  in 
the  ankle.  In  the  hand  beyond  the  carpals  are  five  meta- 
carpal  bones,  each  bearing  a  finger,  and  in  the  foot  beyond 
the  tarsals  are  five  metatarsal  bones,  each  bearing  a  toe.  In 
the  fingers  are  fourteen  phalanges,  and  in  the  toes  are  four- 
teen phalafiges.  The  arms  and  legs  have  the  same  number  of 
bones  in  each,  and  in  their  general  plan  differ  only  in  this,  — 
the  wrist  has  one  more  bone  than  the  ankle,  and  at  the  elbow 
there  is  no  bone  like  the  patella  (knee-cap),  which  protects 
the  front  of  the  knee. 

SHAPES  AND   STRUCTURE  OF  BONES 

Shapes  of  Bones.  The  bones  of  the  human  skeleton  may 
be  classified  as  long  and  short,  fiat  and  cylindrical,  and  irregu- 
lar. This  gives  us  a  great  variety  of  shapes,  but  it  is  usually 
easy  to  see  some  connection  between  the  shape  of  a  bone  and 
its  function. 

Long  bones  give  motion  to  distant  parts  of  the  body,  and  by 
means  of  the  long  bones  great  rapidity  of  motion  through 
long  distances  can  be  brought  about.  The  bones  by  which 
the  hands  and  the  feet  are  moved  so  quickly  and  so  far  are 
the  best  examples  of  long  bones. 


HUMAN  PHYSIOLOGY 


Short   bones    give   free   movement   in   various   direction  5; 
through   short   distances,  and  at  the  same   time  give  great 

strength.  The  bones  of  the 
wrists  and  ankles  and  the  ver- 
tebrae are  the  best  examples  of 
short  bones. 

Cylindrical  bones  are  found 
where  supporting  some  portion 
of  the  body  is  one  of  the  main 
functions  of  the  bone.  The 
bones  of  the  limbs,  of  the 
hands  and  the  feet,  and  the 
clavicles  are  cylindrical  bones. 
Flat  bones  are  usually  either 
protecting  bones  or  bones  to 
which  many  muscles  are  at- 
tached. The  sternum  and  the 
bones  of  the  cranium  are  flat,  protecting  bones.  The  pelvic 
bones  and  the  scapulas  are 
bones  which  are  spread  out  flat 
to  give  room  for  the  muscles. 
Not  only  are  the  flat  bones  made 
so  as  to  give  as  much  room  as 
possible  for  the  muscles,  but  the 
heads  of  the  long  bones  are  ex- 
panded for  the  same  purpose, 
and  nearly  all  bones  have  eleva- 
tions and  processes  (Fig.  21)  to 
which  muscles  can  be  fastened. 
This  is  necessary,  for  there  are  over  five  hundred  muscles 
in  the  body,  most  of  which  are  attached  to  the  skeleton. 
Irregular  bones  usually  have  several  functions.  A  good 


FlG.  20.  The  scapula.  This  flat  bone 
has  many  muscles  attached  to  it.  The 
ridge  strengthens  the  bone  and  its  end 
provides  a  point  against  which  the 
clavicle  can  be  propped. 


FIG.  21.    Vertebrae. 


THE  SKELETON 


39 


example  of  a  bone  of  this  kind  is  a  vertebra.  This  has  a 
round  portion  which  supports  the  weight  of  the  body;  it  has 
a  flattened  ring  of  bone  inclosing  and  protecting  the  spinal 
cord ;  and  it  has  a  flat  spine  behind  and  processes  on  the 
sides,  to  which  the  muscles  of  the  back  are  attached. 

Materials  in  Bone.  A  dead  and  dry  bone  is  composed  of 
a  great  network  of  tough  fibers  and  of  hard  mineral  matter 
that  fills  in  the  spaces  between  the  fibers.  A  bone,  there- 
fore, has  in  it  two  kinds  of  matter,  animal  matter  (the  fibers) 
and  mineral  matter.  About  two  thirds  of  the  weight  of  the 
average  bone  is  mineral  matter  and  one  third  is  animal  mat- 
ter. In  childhood  there  is  a  smaller  proportion  of  mineral 
matter  in  the  bones,  and  in  old  age  the  amount  of  animal 
matter  is  very  small.  By  the  following  experiments  you  can 
find  out  for  yourself  the  proportion  of  animal  and  of  mineral 
matter  in  a  bone,  and  the  function  of  each  kind  of  material : 

Weigh  a  piece  of  dry  bone.  Then  burn  it  in  a  hot  fire.  Notice 
the  smell.  The  animal  matter  in  the  bone  is 
burning.  When  all  the  animal  matter  has  been 
burned  out,  the  bone  will  have  a  grayish  color. 
When  this  is  the  case,  take  it  out  of  the  fire  and 
weigh  it  again.  Of  what  kind  of  matter  is  the 
bone  now  composed?  What  proportion  of  it 
was  animal,  and  what  proportion  mineral  matter? 
Try  to  bend  the  bone,  and  notice  how  easily  it 
crumbles  and  breaks.  What  do  you  think  is  the 
function  of  the  animal  matter  ? 

Dissolve  the  mineral  matter  out  of  the  drum- 
stick of  a  chicken  or  turkey  by  soaking  it  in 
weak  hydrochloric  acid.1  Then  examine  the  bone, 
and  note  that  it  is  the  same  size  and  shape  as  be- 
fore. Try  to  bend  it  and  you  will  find  that  it  is 
as  limber  as  a  piece  of  rubber.  Of  what  is  the 
bone  now  composed  ?  What  is  the  function  of  the 
mineral  matter  of  the  bone? 


FIG.  22.  A  femui 
with  the  mineral  mat- 
ter removed. 


1  Any  weak  acid,  or  strong  vinegar,  may  be  used  in  this  experiment. 


40 


HUMAN  PHYSIOLOGY 


From  these  two  experiments  you  will  understand  that  the 
mineral  matter  gives  to  tJie  bones  tJie  stiffness  and  firmness 
which  enables  them  to  support  tJie  body,  and  the  animal 
matter  gives  the  toughness  which  keeps  them  from  breaking. 

Structure  of  Bones.  The  shafts  of  the  long  bones  and  a 
thin  layer  on  the  surface  of  all  the  bones  are  composed  of 


FIG.  23.  A  is  a  portion  of  the  shaft  of  a  long  bone.  B  is  a  cross-section  of  a  small 
portion  of  the  same  bone  more  highly  magnified,  showing  more  clearly  the  canals  in 
the  compact  bone  and  the  small  cavities  (lacunce)  in  which  the  bone  cells  lie. 

compact  bone.  The  remainder  of  the  skeleton  is  composed 
of  spongy  bone.  The  spongy  bone  is  filled  with  small  cavi- 
ties, like  the  holes  in  a  sponge.  The  compact  bone  when 
looked  at  with  the  unaided  eye  appears  solid,  but  when 
examined  under  the  microscope  even  this  hard  bone  is  seen 
to  be  full  of  very  small  canals.  Through  these  canals  the 


THE  SKELETON 


41 


blood  vessels  reach  to  every  part  of  the  bone,  carrying  nour- 
ishment to  the  bone  cells. 

The  Cavities  in  the  Long  Bones.  To  provide  room  for  the 
attachment  of  all  the  muscles  and  to  have  sufficient  strength 
for  the  support  of  the  body,  the  bones  must  be  large.  At 
the  same  time  it  would  be  objectionable  to  have  very  heavy 
bones,  for  the  muscles  would  find  great  difficulty  in  moving 
them  about.  The  small  cavities  in  spongy  and  compact  bone 
assist  in  decreasing  the  weight  of  the  skeleton.  To  lighten 


FIG.  24.     Experiment  showing  that  a  hollow  cylindrical  bone  is  strong. 

it  still  more,  large  cavities  are  hollowed  out  in  the  long  bones 
of  the  limbs.  That  a  hollow  cylinder  is  stronger  than  the 
same  material  in  a  solid  form,  you  can  prove  by  the  follow- 
ing experiment : 

Set  a  sheet  of  paper  on  end  and  lay  a  book  on  it.  Will  it 
support  the  book?  Fold  the  paper  as  tightly  as  possible,  so  that  it 
will  be  in  the  form  of  a  small,  solid  bone.  Will  it  now  support  the 
book?  Now  roll  the  paper  into  a  hollow  cylinder  and  place  your 
book  upon  it.  Will  it  support  a  heavier  weight  than  it  would  before 
it  was  rolled  into  this  form  ?  Does  it  contain  any  more  material  or 
is  it  any  heavier? 

Nature  uses  a  hollow  cylinder  not  only  in  the  skeleton, 
but  in  other  structures  where  she  wishes  to  combine  strength 


42  HUMAN  PHYSIOLOGY 

and  lightness.  Stalks  of  grasses  and  grains  are  hollow,  and 
so  strong  is  a  wheat  stalk  that  it  has  a  height  four  hundred 
times  as  great  as  its  diameter,  and  carries  the  heavy  head  of 
grain  without  breaking,  although  it  is  blown  about  and  bent 
by  the  wind.  Man  also  uses  hollow  tubes  in  the  framework 
of  bicycles,  and  in  other  places  where  he  wants  strength 
without  great  weight. 

Bone  Marrow.  The  large  cavities  of  the  long  bones  and 
the  smaller  cavities  of  the  spongy  bone  are  filled  with  bone 
CARTILAGE  marrow.  The  marrow  in  the  larger  cavi- 
ties contains  blood  vessels,  nerves,  connec- 
tive tissue,  and  fat.  The  marrow  of  the 
spongy  bone  contains  less  fat,  and  in  it  the 
red  corpuscles  of  the  blood  are  formed. 
Because  of  the  large  quantity  of  fat  which 
it  contains,  the  marrow  of  the  larger  cavi- 
ties is  yellow  in  color ;  the  marrow  in  the 
spongy  bone,  because  of  the  large  number 
of  red  corpuscles  which  it  contains,  usually 
has  a  reddish  hue. 

The  Periosteum.      Pick  the  surface  of  a 
fresh  bone  with  the  point  of  a  knife,  and 
you  can  lift  a  thin  covering  or  membrane. 
This  is  the  periosteum.     It  is  made  of  a 
network  of  connective  tissue  fibers,  closely 
woven  together  over   the   surface  of   the 
FIG.  25.  Longitudinal    bone.    Among  the  fibers  of  the  periosteum 
section  of  the  humems.   are  many  of  the  blood  vessels  which  carry 
nourishment  to  the  bones,  and  if  the  periosteum  is  destroyed, 
the  bone  under  it  will  die.1 

1 A  bone  grows  in  thickness  by  having  layers  of  new  bone  material  laid  down 
on  the  surface  of  the  bone  under  the  periosteum. 


SPONGY 
'BONE 


THE  SKELETON  43 

Summary.  The  bones  support  the  body,  protect  delicate 
organs,  and  act  as  levers  by  means  of  which  the  muscles  move 
the  body.  There  are  206  bones  in  the  human  skeleton,  —  28 
in  the  skull,  58  in  the  skeleton  of  the  trunk,  and  120  in  the 
skeleton  of  the  limbs. 

In  respect  to  their  shape,  bones  are  classified  as  long  and 
short,  flat  and  cylindrical,  and  irregular.  Long  bones  give 
rapid  motion  through  long  distances.  Short  bones  combine 
strength  and  freedom  of  movement.  Cylindrical  bones  are 
supporting  bones,  and  flat  bones  protect  delicate  organs  or 
have  many  muscles  attached  to  them.  Irregular  bones  usually 
have  several  different  functions. 

Bones  are  one  third  animal  matter,  which  makes  them 
tough,  and  two  thirds  mineral  matter,  which  gives  them 
their  stiffness  and  rigidity.  The  cavities  in  the  bones  help  to 
lighten  them  and  at  the  same  time  permit  them  to  retain 
sufficient  strength  to  support  the  body. 

Bone  marrow  contains  fat,  blood  vessels,  connective  tissue, 
and  nerves.  The  yellow  marrow  has  in  it  much  fat.  The  red 
marrow  contains  less  fat,  and  in  it  the  red  blood  corpuscles  are 
formed.  The  periosteum  carries  many  of  the  blood  vessels 
that  nourish  the  bone. 

QUESTIONS 

Give  three  functions  of  the  skeleton.  How  many  bones  are  in  the 
body  ?  Into  how  many  groups  are  they  divided  ?  How  many  bones 
are  there  in  each  group  ? 

How  many  bones  are  in  the  skull?  'in  the  cranium?  in  the  ears?  in 
the  face  ?  Name  some  of  the  bones  of  the  skull. 

How  many  and  what  bones  are  in  the  spinal  column  ?  Give  two 
qualities  that  the  spinal  column  must  have.  Give  two  advantages 
that  come  from  having  the  spinal  column  composed  of  many  parts. 


44  HUMAN  PHYSIOLOGY 

Where  is  the  sternum  ?  How  many  ribs  are  there  ?  What  is  a 
true  rib  ?  a  false  rib  ?  a  floating  rib  ?  Give  two  uses  of  the  ribs. 

Name  the  shoulder  bones.  To  what  is  the  scapula  attached? 
What  is  the  function  of  the  clavicle  ?  What  bones  compose  the 
pelvis  ?  Give  three  functions  of  the  pelvis.  Compare  the  skeletons 
of  the  arm  and  of  the  leg. 

Give  four  shapes  of  bones,  with  the  functions  of  bones  having  each 
of  these  shapes.  Give  examples  of  bones  of  each  shape. 

What  two  kinds  of  material  in  bone  ?  What  proportion  of  a  bone 
is  mineral  matter  ?  animal  matter  ?  What  is  the  function  of  the 
mineral  matter  ?  of  the  animal  matter  ?  At  what  time  of  life  is  there 
little  mineral  matter  in  the  bones  ?  little  animal  matter  ? 

Where  in  the  skeleton  is  the  compact  bone  found  ?  spongy  bone  ? 
How  do  compact  and  spongy  bone  differ? 

Why  is  it  necessary  that  the  bones  should  have  considerable  size  ? 
What  would  be  the  objection  to  having  large  solid  bones  ?  How 
have  the  large  bones  been  lightened  without  too  greatly  weakening 
them  ? 

Of  what  is  bone  marrow  composed  ?  Where  is  red  bone  marrow 
found  ?  yellow  bone  marrow  ?  How  does  one  kind  of  marrow  differ 
from  the  other?  What  is  the  periosteum?  What  happens  to  the 
bone  when  the  periosteum  is  destroyed  ? 


Of  what  is  the  animal  matter  in  a  living  bone  composed  (page  8)  ? 
Do  the  bones  of  an  old  person  or  of  a  little  child  bend  more  easily  ? 
Why  ?  Which  breaks  more  easily  ?  Why  ?  Which  heals  more 
easily  after  it  is  broken  r  Why  ? 

Is  a  hollow  iron  post  as  strong  as  a  solid  iron  post  of  the  same 
size  ?  How  many  times  as  high  as  its  own  diameter  is  the  tallest 
smokestack  or  tower  that  you  know  ? 

What  part  of  the  skeleton  is  incomplete  in  a  little  baby? 


CHAPTER  V 

THE  SKELETON  (Continued) 
JOINTS 

EACH  bone  can  support  the  part  of  the  body  in  which  it 
is  located,  but  to  form  a  skeleton  for  the  support  of  the  body 
as  a  whole,  the  bones  must  be  joined  together.  The  places 
where  the  bones  come  together  are  the  joints.  These  are 
divided  into  two  great  classes,  —  immovable  and  movable 
joints. 

Immovable  Joints.  Immovable  joints  are  found  in  portions 
of  the  body  where  movement  between  the  bones  is  not  neces- 
sary, and  where  great  strength  and  firmness  are  required  in 
the  skeleton.  In  the  cranium  all  the  bones  are  solidly  joined 
to  protect  the  brain,  and  the  joints  are  immovable.  The  joint 
between  the  two  pelvic  bones,  and  the  joints  between  the 
pelvic  bones  and  the  sacrum,  are  other  examples  of  immov- 
able joints.  All  the  bones  of  the  pelvis  are  thus  firmly  united 
in  one  solid  support  for  the  body.  In  our  own  bodies  we 
overlook  the  immovable  joints  because  there  is  no  movement 
at  these  places,  but  in  a  skeleton  this  kind  of  joint  may  easily 
be  observed. 

Necessity  for  Movable  Joints.  Most  of  the  joints  in  the 
skeleton  are  movable.  It  is  necessary  that  they  should  be, 
for  it  is  only  at  the  movable  joints  that  the  body  can  bend. 
Without  movable  joints  you  could  not  close  your  hand ;  you 

45 


46  HUMAN  PHYSIOLOGY 

could  not  bring  your  hand  to  your  mouth ;  you  could  not  sit ; 
and  you  could  not  walk.  Without  movable  joints  it  would 
not  be  possible  for  one  part  of  the  body  to  be  moved  without 
moving  the  whole  body.  You  will  understand,  if  you  think 
about  it,  that  with  the  whole  skeleton  united  solidly  in  one 
piece,  our  muscles  could  not  move  the  body  at  all.  With  a 
skeleton  having  movable  joints,  they  lift  the  body  about,  one 
part  at  a  time;  but  without  the  bending  at  the  joints,  the 
muscles  would  have  no  more  power  of  lifting  the  body  than 
you  have  of  lifting  a  chair  in  which  you  are  sitting. 

Kinds  of  Movable  Joints.  Movable  joints  are  of  three1 
principal  kinds,  —  ball-and-socket  joints,  hinge  joints,  and 
gliding  joints. 

In  ball-and-socket  joints  a  ball,  or  rounded  end,  of  one  bone 
fits  into  a  socket,  or  cup-like  hollow,  in  the  other  bone.  The 
shoulder  joint  and  the  hip  joint  (Fig.  27)  are  good  examples 
of  ball-and-socket  joints.  This  kind  of  joint  allows  motion 
freely  in  any  direction,  as  you  can  observe  by  swinging  the 
arm  about  at  the  shoulder,  or  the  leg  at  the  hip. 

Hinge  joints  do  not  allow  motion  in  all  directions,  but  only 
in  two  opposite  directions,  —  the  same  movement  that  a  knife 
blade  has  in  opening  and  closing.  The  elbow  and  knee  joints, 
the  first  two  joints  of  the  fingers  and  toes,  and  the  joints  of 
the  lower  jaw  are  examples  of  hinge  joints.  What  kind 
of  a  joint  is  at  the  base  of  the  metacarpal  bone  that  bears  the 
thumb  ? 

In  gliding  joints  the  bones  move  or  glide  only  a  little 
on  each  other.  The  joints  between  the  small  bones  of  the 
ankles  and  the  wrists  are  good  examples  of  gliding  joints. 

1  The  joints  between  the  bodies  of  the  vertebrae  are  intermediate  between  im- 
movable and  movable  joints.  In  them  the  bones  do  not  slide  on  each  other,  but 
the  thick  and  elastic  cartilages  (Fig.  21)  permit  considerable  bending. 


THE  SKELETON 


47 


CARTILAGE  AND    LIGAMENTS 

Cartilage.  By  far  the  greater  portion  of  the  human  skele- 
ton is  bone,  but  a  small  part  of  it  is  composed  of  cartilage^-  and 
ligaments.  Cartilage  (Fig.  26)  is 
a  smooth  white  substance  always 
found  covering  the  ends  of  the 
bones  at  the  joints.  In  a  movable 
joint  each  bone  has  its  own  carti- 
lage, and  the  surfaces  where  the 
two  cartilages  rub  together  are 
kept  moist  by  an  oily  liquid.  The 
smooth  cartilage  and  the  oily  fluid 
keep  down  friction  in  the  movable 
joints  and  cause  them  to  work 
smoothly  and  noiselessly. 

In  immovable  joints,  a  piece  of 
cartilage  grows  in  between  the 
two  bones  and  firmly  unites  them. 
Cartilage  is  found  also  in  the  front 
portion  of  each  rib  (Fig.  19).  This 
makes  the  ribs  more  springy  and 
less  likely  to  be  broken  by  pressure 
or  by  a  blow  on  the  chest. 

Ligaments.  Around  the  joints  are  tough  bands  of  con- 
nective tissue  called  ligaments.  In  parts  of  the  body  like  the 

1  When  the  skeleton  is  being  formed  in  the  body,  it  is  at  first  composed  of 
cartilage.  This  changes  to  bone  until  only  a  thin  layer  of  cartilage  on  the  ends 
of  the  bones  remains.  As  long  as  a  bone  is  growing,  however,  there  is  some 
cartilage  in  it.  Thus,  in  youth,  there  are  in  the  shaft  of  a  long  bone  one  or  more 
narrow  rings  of  cartilage.  This  cartilage  grows  and  keeps  turning  to  bone  on 
each  side,  causing  the  bone  to  increase  in  length.  Finally  the  rings  of  cartilage 
turn  to  bone  and  there  is  no  more  growth  in  the  length  of  the  bone. 


FIG.  26.  Cartilage.  Cartilage 
has  a  connective  tissue  covering 
(a)  similar  to  the  periosteum  on 
a  bone.  The  cartilage  cells  (6) 
build  around  themselves  a  whitish, 
elastic  substance  (c)  which  forms 
the  ground  material  of  cartilage. 


48 


HUMAN  PHYSIOLOGY 


knee,  elbow,  ankle,  and  wrist, 
the  number  of  ligaments  about 
the  joints  is  astonishingly  great. 
Their  function  is  to  Jiold  tlie  bones 
of  the  skeleton  together. 

HOW    THE     SKELETON    PROTECTS 
THE  BRAIN 

In  all  ordinary  circumstances 
the    cranium    shields    the    brain 
FIG.  27.   The  ligaments  of  the  hip    from    outside    injury,     and    the 
J°mt-  whole    skeleton   is   arranged   to 

protect  the  brain  from  injury  by  jarring.  This  is  necessary 
because  the  brain  is  so  soft  and  delicate  an  organ  that  not- 
withstanding the  protection  given  to  it  by  the  membranes 
and  fluid  about  it  (page  26),  it  is  shaken  about  and  injured 
by  any  violent  jarring  of  the  head.  When  you  have  a  head- 
ache after  having  bumped  your  head,  the  brain  has  been 
injured;  and  death  sometimes  follows  a  blow  on  the  head, 
even  when  the  skull  has  not  been  fractured,  because  of  injury 
to  the  brain. 


FIG.  28.     Pressing  on  an  arched  stick. 


FIG.  29.     The  arch  of  the  foot. 


If   the  head  were  jarred   every  time   the  feet   strike  the 
ground  in  walking  and  running,  it  would  surely  be  harmful 


THE  SKELETON" 


49 


to  the  brain.     To  prevent  this  jarring,  the  skeleton  has  in  it 
three  devices  that  give  springiness  to  the  whole  frame. 

The  Arch  of  the  Foot.  Press  on  a  curved  stick  or  a  piece 
of  barrel  hoop  as  shown  in  Figure  28,  and  notice  how  much 
springiness  the  arch  gives  it.  The  bones  of 
the  human  foot  form  an  arch  on  which  the 
weight  of  the  body  falls  when 
the  body  is  in  a  standing  position. 
In  walking  and  running,  there- 
fore, the  arch  of  the  foot  acts  as 
a  spring  under  the  body. 

The  Curves  of  the  Spinal 
Column.  Strike  the  floor  with 
a  straight  stick  held  as  in  Figure 
30  and  your  hand  will  be  jarred. 
But  strike  the  floor  with  a  curved 
stick  held  in  the  same  way,  and 
you  will  find  that  the  curve  will 
give  a  springiness  to  the  stick 
that  prevents  the  hand  from  being 
jarred.  The  double  curve  of  the 
spinal  column  (Fig.  18)  makes  it 
springy,  and  so  protects  the  head 
from  the  jar  when  the  feet  strike 
the  ground.  You  can  get  an  idea 
of  the  usefulness  of  these  curves 
by  imagining  how  much  worse 
your  brain  would  be  shaken  up 
when  you  run  and  jump  if  your  head  were  carried  on  the 
end  of  a  straight,  stiff  bone  instead  of  on  your  spinal  column.1 

1  Jump  with  the  legs  held  straight  and  stiff.     Then  jump  with  the  legs  bent 
at  the  knees,  and  notice  the  difference  in  the  amount  of  jar  the  body  receives. 


FIG.  30.  This 
straight  stick 
jars  the  hand. 


FIG.  31.  This 
curved  stick 
springs  down 
and  does  not 
jar  the  hand. 


50  HUMAN  PHYSIOLOGY 

Cartilages.  The  cartilages  between  all  the  joints,  but 
especially  the  thick  cartilages  between  the  vertebrae  (Fig.  21), 
act  like  rubber  pads  in  giving  elasticity  to  the  skeleton.  If 
you  have  worn  shoes  with  rubber  heels,  or  have  walked  on  a 
rubber  mat,  you  will  know  at  once  how  these  cartilages  pre- 
vent jarring  of  the  brain. 

These  three  devices,  along  with  the  half-bent  joints  of  the 
legs,  give  springiness  to  the  skeleton  and  protect  the  brain. 
How  well  this  work  is  done,  you  may  know  from  the  fact 

that  boys  and  girls  in  their  play  run 
about  and  jump,  and  sometimes  fall 
so  hard  that  the  bones  of  the  body 
are  broken,  and  yet  it  is  not  often 
that  the  brain  is  injured. 

THE   SKELETONS  OF   OTHER  VERTE- 
BRATES 

Similarity  of  Human  and  Other 
Vertebrate  Skeletons.  In  the  skele- 
tons of  all  vertebrates,  a  spinal 
column  and  skull  are  found.  All  of 
them  except  the  amphibians  have 
ribs.  Shoulder  and  pelvic  bones  to 
which  the  limbs  are  attached  are 
found  in  almost  all  of  them.  The 
limbs  of  vertebrates  are  built  on  the 
same  general  plan,  but  they  are  used 

skeleton  !f  anLng-u.an.        in  so  manY  different  ways  that  the 
skeletons  of  the  limbs  may  seem  to 

be  very  different.      Certain  bones  may  be  much  longer  than 
they  are  in  man,  as  the  phalanges  in   the  wings  of  a  bat. 


THE  SKELETON  51 

Often  bones  may  be  united  as  are  the  tibia  and  the 
fibula  in  the  frog,  and  the  carpal  and  metacarpal,  and  the 
tarsal  and  metatarsal  bones  of  many  animals.  Sometimes 
we  have  the  wrong  idea  of  a  limb  until  we  study  it  closely. 
Thus,  in  the  front  limb  of  the  horse,  the  foot  corresponds 
to  one  finger  on  our  hand,  the  hoof  to  a  finger  nail,  and  the 
one  metatarsal  is  very  long,  so  that  what  seems  to  be  the 
knee  is  really  the  wrist.  In  birds  the  tarsal  and  metatarsal 
bones  are  united  and  elongated  and  in  a  chicken  the  ankle 
joint  is  often  thought  to  be  the  knee.  In  some  ways  the 
limbs  of  these  animals  are  very  different  from  the  limbs 
of  man,  but  all  the  principal  bones  in  them  correspond  to 
the  principal  bones  in  the  human  arms  and  legs. 

Differences  between  the  Human  and  Other  Vertebrate 
Skeletons.  Of  all  the  vertebrates,  monkeys  and  apes  have 
skeletons  most  nearly  like  the  skeleton  of  man.  But  although 
an  ape's  skeleton  has  in  it  every  bone  that  is  found  in  the 
human  skeleton,  yet  there  is  no  difficulty  in  distinguishing 
between  the  two. 

An  ape  has  less  intelligence  than  a  man,  and  its  brain  and 
cranium  are  much  smaller.  The  jaws  of  an  ape  are  much 
longer  and  heavier  than  they  are  in  man,  the  teeth  are 
larger,  and  the  front  teeth  slant  forward. 

The  human  spinal  column  has  a  backward  turn  at  the 
top  that  causes  the  skull  to  balance  on  top  of  the  spinal  col- 
umn when  the  body  stands  upright.  The  spinal  column  of 
an  ape  lacks  this  backward  curve,  and  when  an  ape  stands 
up  its  head  sticks  out  forward.  The  muscles  of  the  neck, 
shoulders,  and  back,  therefore,  have  heavy  work  to  keep  the 
head  from  falling  forward  when  the  body  stands  erect. 

The  pelvis  and  femurs  of  man  are  also  fitted  for  an  upright 
carriage  of  the  body.  Man  is  a  very  tall  animal  for  his  size, 


FIG.  33.  Vertebrate  limbs.  A  is  the  human  leg;  B,  the  human  arm-  C,  the  fore 
leg  of  a  horse ;  D,  the  wing  of  a  bird ;  E,  the  foot  of  a  bird ;  F,  the  hind  leg  of  a  frog  • 
G,  the  wing  of  a  bat ;  H,  the  fore  leg  of  a  tortoise. 


THE  SKELETON  53 

and  he  has  only  two  feet  to  balance  himself  on.  The  human 
pelvis  is,  therefore,  wide,  and  the  heads  of  the  femurs  are 
turned  inward.  The  feet  are  thus  spread  apart,  making  it 
easier  to  keep  the  balance  of  the  body.  Shut  your  eyes  and 
stand  with  your  feet  wide  apart.  Then  shut  your  eyes  and 
stand  with  your  feet  close  together,  and  you  will  understand 
the  advantage  of  this  arrangement. 

The  arms  of  the  ape  are  proportionately  much  longer  than 
the  arms  of  man,  and  the  legs  are  shorter.  In  man  the  arms 
reach  about  halfway  between  the  hip  and  the  knee.  In  apes 
they  reach  to  the  knee,  and  in  some  species  even  to  the 
ground. 

In  apes  all  the  metacarpal  and  metatarsal  bones  are  very 
long  except  the  first  one,  which  is  very  short.  This  sets  the 
thumbs  and  great  toes  far  down  on  the  sides  of  the  hands 
and  feet,  and  in  reality  gives  the  apes  neither  true  hands 
(with  thumbs  opposing  the  fingers)  for  grasping,  nor  feet  for 
walking,  as  we  find  in  man;  but  long  organs  halfway  between 
hands  and  feet,  with  which  the  ape  holds  to  large  branches 
as  it  climbs  among  the  trees. 


HYGIENE  OF  THE  SKELETON 

As  the  body  grows,  mineral  matter  is  gradually  deposited 
in  the  bones  and  the  skeleton  becomes  harder.  During  child- 
hood the  bones  are  flexible  and  it  is  easy  to  bend  them  and 
change  their  shapes ;  but  after  the  skeleton  has  hardened,  it 
is  exceedingly  difficult  to  change  the  shape  of  the  bones. 

It  is  very  important,  therefore,  that  the  skeleton  be  kept 
in  proper  position  during  childhood  and  youth.  The  general 
carriage  of  the  body  cannot  be  well  understood  until  we 
have  studied  the  muscles,  so  here  we  shall  point  out  only 


54  HUMAN  PHYSIOLOGY 

a  few  ways  in  which  different  bones  of  the  body  may  be 
bent  out  of  their  proper  shape. 

Allowing  a  baby  to  stand  up  and  walk  too  soon  may  cause 
him  to  become  bow-legged,  and  lifting  or  carrying  heavy  loads 
may  have  the  same  effect  on  older  children.  Heavy  work 
done  by  the  young  is  likely  to  pull  the  points  of  the  shoulders 
downward  and  forward,  causing  round  shoulders.  Anything 
carried  habitually  on  one  side  may  cause  the  spinal  column  to 
be  bent  over  to  that  side.  It  has  been  found  that  many 
school  children  have  slight  curvature  of  the  spine  from 
always  carrying  their  books  on  the  same  arm,  and  very 
many  people  have  one  shoulder  or  hip  a  little  higher  than 
the  other.  Boys  sometimes  wear  belts  that  are  drawn  too 
tight  around  the  waist,  instead  of  resting  on  the  hips.  These, 
or  any  tight  clothing  around  the  waist,  may  bend  in  the 
lower  ribs.  This  is  very  injurious,  for  it  presses  on  the 
organs  which  are  packed  in  the  abdominal  cavity. 

You  should  avoid  all  these  unhygienic  practices,  and  others 
which"  you  will  think  of  for  yourselves,  such  as  stooping 
over  your  desk,  or  sitting  sideways  in  your  seat  with  one 
shoulder  higher1  than  the  other,  while  you  study  or  write. 
You  should  take  especial  care  to  form  the  habit  of  carrying 
the  body  erect;  for  if  the  bones  are  permitted  to  harden  in  a 
stooping  position,  it  is  almost  certain  that  you  will  go  through 

1To  THE  TEACHER:  Much  real  damage  as  well  as  a  great  deal  of  discomfort 
may  be  caused  by  having  seats  and  desks  that  are  too  low  or  too  high  for  the 
pupils.  Writing  on  desks  that  are  too  high  will  throw  one  shoulder  higher  than 
the  other  and  cause  lateral  curvature  of  the  spine.  Bending  over  a  desk  that  is 
too  low  will  give  a  stooping  carriage  to  the  body.  Sitting  in  seats  so  high  that 
the  feet  cannot  touch  the  floor  causes  stooping  and  very  great  weariness. 
Where  the  school  authorities  fail  to  provide  proper  desks,  the  teacher  should  see 
that  the  younger  children  have  foot  rests  and  should  do  everything  in  his  power 
to  have  all  his  pupils  properly  seated. 


THE  SKELETON  55 

life  with  a  stooping  carriage,  your  sternum  and  ribs  dropping 
down  and  crowding  your  heart  and  lungs.  If  you  have  any 
work  that  compels  you  to  stoop  as  you  do  it,  stop  once  in  a 
while,  straighten  yourself  up,  and  take  several  deep  breaths ; 
in  addition,  make  a  special  point  of  holding  the  body  erect 
while  not  at  work. 

Broken  Bones.  If  the  two  ends  of  a  broken  bone  are 
placed  together,  the  bone  cells  soon  cover  the  surface  of  the 
broken  ends  with  a  jelly-like,  white  material.  In  a  few  days 
this  begins  to  harden,  and  soon  the  two  parts  are  firmly 
united.  The  only  thing  we  can  do  to  help  nature  in  this 
process  is  to  put  the  broken  ends  together,  and  keep  them 
together  until  the  fracture  is  healed.  Of  course  a  physician 
must  be  called  to  set  a  broken  bone,  but  the  patient  needs 
intelligent  care  until  the  physician  arrives.  If  an  arm  or 
a  leg  is  broken,  stretch  it  out  straight  on  a  pillow.  If  the 
person  must  be  moved,  tie  a  pillow  about  the  limb,  or  wrap 
a  blanket  or  a  coat  around  it,  and  then  tie  umbrellas  or  canes 
about  it  to  keep  it  straight.  Often  there  are  sharp  points  on 
the  broken  ends  of  bones.  In  lifting  the  person,  take  care 
that  the  limb  is  not  bent  at  the  fracture •,  or  the  sharp  ends  of 
the  broken  bone  may  cut  the  muscles,  blood  vessels,  or 
nerves. 

Dislocations  and  Sprains.  When  the  ligaments  (and  some- 
times the  muscles  and  nerves  also)  around  a  joint  are  broken, 
and  the  bones  slip  out  of  place,  we  have  a  dislocation.  A 
few  people  have  some  joints  with  sockets  so  shallow  that  the 
bones  may  be  dislocated  without  breaking  the  ligaments,  but 
such  joints  are  not  common.  When  a  bone  is  dislocated,  it 
must  be  put  back  into  its  place  and  kept  there  until  the  liga- 
ments grow  again  about  the  joint.  Usually  only  a  physician 
can  get  a  dislocated  bone  back  into  place  without  danger  to 


56  HUMAN  PHYSIOLOGY 

the  patient,  and  he  should  be  called  before  the  parts  become 
swollen. 

When  a  joint  is  sprained,  some  of  the  ligaments  around  it 
are  broken  and  torn  loose,  but  the  bones  are  not  dislocated. 

Treatment  of  Dislocations  and  Sprains.  Until  a  physician 
can  be  called,  both  dislocated  and  sprained  joints  should  be 
bathed  in  either  hot  or  cold  water,  or,  better  still,  in  hot  and 
cold  water  alternately.  This  will  help  to  keep  the  injured 
part  from  swelling  and  becoming  painful. 

A  dislocated  or  sprained  joint  should  not  be  rested  all  the 
time,  but  should  be  exercised,  even  if  the  movement  causes 
great  pain.  If  the  joint  is  not  exercised,  it  will  become  much 
swollen  with  liquids  from  the  blood,  and  will  be  very  painful. 
Exercise  helps  to  keep  up  a  good  circulation  of  the  blood 
through  the  part,  and  this  carries  away  the  broken  tissue  and 
dead  cells,  and  helps  in  every  way  to  hasten  the  healing  of 
the  injury.  But  after  a  dislocation,  great  care  must  be  used 
that,  in  exercising,  the  injured  parts  are  not  again  dislocated. 
A  dislocated  joint  should  be  well  bandaged  to  keep  the  bones 
in  place,  and  then  exercised  in  such  a  way  that  there  will  be 
no  danger  of  dislocating  it  again. 

Tobacco  and  the  Skeleton.  The  bones  are  built  up  and 
grow  through  the  manufacture  of  bone  materials  by  the  cells 
(page  8).  Tobacco  seems  to  injure  the  cells  which  do  this 
work,  for  young  persons  who  use  tobacco  are  usually  stunted 
in  their  growth.  We  know  that  tobacco  injures  the  heart  and 
the  digestive  organs,  and  it  may  be  that  it  injures  the  bone  cells 
by  preventing  them  from  getting  a  good  supply  of  food  and 
oxygen.  Possibly  the  tobacco  itself  injures  the  bone  cells. 
However  the  harm  is  done,  we  are  sure  that  it  is  done,  for 
the  bones  of  young  tobacco  users  do  not  grow  as  they  should. 

Summary.      There   are   two    great   classes  of   joints,  im- 


THE  SKELETON-  57 

movable  and  movable.  Immovable  joints  are  found  in  the 
skeleton  where  motion  is  not  necessary,  but  firmness  and 
strength  are  required.  Movable  joints  are  necessary  that  the 
different  body  parts  may  have  motion.  The  three  principal 
kinds  of  movable  joints  are  ball-and-socket  joints,  hinge  joints, 
and  gliding  joints. 

The  ends  of  the  bones  are  covered  with  a  smooth,  white 
substance  called  cartilage.  In  the  movable  joints  this  is 
kept  moist  with  an  oil-like  liquid,  which  causes  the  joints  to 
work  smoothly.  At  the  joints  the  bones  are  tied  together 
with  strong  connective  tissue  ligaments. 

The  arch  of  the  foot,  the  curves  of  the  spinal  column,  and 
the  cartilages  in  the  skeleton  and  the  half-bent  knee  joints 
keep  the  brain  from  being  jarred  as  we  walk  and  run. 

The  human  skeleton  resembles  other  vertebrate  skeletons 
in  having  a  spinal  column,  skull,  ribs,  shoulder  and  pelvic 
bones,  and  two  pairs  of  limbs.  The  bones  in  other  vertebrate 
limbs  often  differ  markedly  from  the  bones  in  the  human 
limbs,  but  in  all  these  limbs  the  same  general  plan  of  the 
skeleton  is  present.  Man's  skeleton  differs  from  an  ape's  in 
the  skull,  spinal  column,  pelvis,  and  femurs,  the  length  of 
the  arms,  and  in  the  hands  and  feet. 

During  childhood  and  youth  the  bones  are  easily  bent,  and 
it  is  very  important  that  they  be  kept  in  proper  position.  A 
broken  limb  should  not  be  allowed  to  bend  at  the  fracture. 
In  a  dislocation  or  a  sprain  the  ligaments  about  the  joint  are 
broken.  A  joint  that  has  been  injured  in  this  way  should  be 
treated  with  hot  or  cold  water  and  carefully  exercised. 

Tobacco  keeps  the  bones  of  the  skeleton  from  reaching 
their  full  growth. 


58  HUMAN  PHYSIOLOGY 


QUESTIONS 

What  is  a  joint  ?  What  are  the  two  great  classes  of  joints  ?  Where 
are  immovable  joints  found?  Give  examples  of  immovable  joints. 

Why  are  movable  joints  necessary?  Name  three  kinds  of  mov- 
able joints.  Explain  what  movement  each  kind  of  movable  joint 
allows.  Give  examples  of  each  kind. 

Where  is  cartilage  found?  What  is  its  use  in  the  movable  joints? 
What  is  a  ligament  and  what  is  its  function? 

Why  is  it  important  that  the  skeleton  should  have  springiness? 
Name  three  devices  for  giving  springiness  to  the  skeleton. 

Mention  some  ways  in  which  the  human  skeleton  resembles  other 
vertebrate  skeletons.  Mention  five  ways  in  which  the  human  skeleton 
differs  from  the  skeleton  of  an  ape. 

Why  is  it  important  that  the  skeleton  be  kept  in  proper  shape  dur- 
ing early  life  ?  Mention  four  ways  in  which  parts  of  the  skeleton  may 
be  deformed. 

How  would  you  care  for  a  person  with  a  fractured  limb?  What  is 
a  dislocation  ?  a  sprain  ?  What  is  the  best  treatment  for  a  dislocation 
or  a  sprain  ? 

What  effect  has  tobacco  on  the  skeleton? 


Carefully  measure  your  height  in  the  morning.  Then  measure  it 
again  at  night  after  you  have  been  moving  about  all  day.  Are  you 
taller  in  the  morning  or  in  the  evening?  Why? 

Do  you  know  any  animals  that  have  the  skeleton  on  the  outside  of 
the  body?  What  great  advantage  is  this  to  these  animals?  What 
do  crabs,  lobsters,  crayfish,  and  many  insects  find  it  necessary  to  do 
when  the  body  increases  in  size  ?  An  earthworm  has  no  skeleton. 
How  does  it  cause  its  body  to  move  in  crawling? 


CHAPTER   VI 

THE   MUSCLES 

THE  skeleton  supports  the  body.  The  muscles  move  it. 
When  we  think  of  a  living  animal,  we  think  of  it  as  having 
the  power  to  move.  Yet  without  muscles  we  and  all  the 
animals  we  see  about  us  would  lie  quiet,  like  dead  matter. 
It  is  by  the  power  of  the  muscles  that  the  giant  whale  is 
driven  through  the  sea,  and  the  wild  bird  is  carried  through 
the  air.  Muscles  cause  the  wings  of  the  mosquito  to  vibrate 
faster  than  the  eye  can  see ;  they  move  the  creeping  snail. 
The  muscles  carry  our  feet  along,  they  lift  our  arms,  they 
keep  our  hearts  beating  night  and  day.  The  power  by  wJiich 
a  muscle  causes  movement  lies  within  its  cells.1 

The  Muscles.  The  skeleton  is  the  framework  of  the  body, 
and  the  muscles  are  stretched  on  the  framework,  sliding 
smoothly  and  noiselessly  over  one  another  in  their  move- 
ments. They  form  the  chief  part  of  the  flesh  which  rounds 

1  The  tissues  that  we  have  studied  up  to  this  time  are  the  supporting  tissues  of 
the  body,  and  the  pupil  should  get  clearly  in  mind  the  difference  between  them 
and  the  other  tissues.  The  function  of  bone,  cartilage,  and  connective  tissue  is 
to  support  the  body.  Since  this  work  is  too  heavy  for  soft  cells,  the  cells  of  sup- 
porting tissues  become  builders  and  construct  a  great  framework  to  support  the 
body.  The  bone  cells  build  bone  fibers  and  hard  mineral  matter.  The  con- 
nective tissue  cells  build  tough  connective  tissue  fibers,  and  the  cartilage  cells 
build  the  groundwork  of  cartilage.  Supporting  tissues  are  composed  of  cells  and 
materials  which  the  cells  have  built.  Other  tissues  are  composed  entirely  of  cells. 
Muscle  tissue  is  composed  of  muscle  cells,  the  largest  and  most  active  cells  in 
the  body. 

59 


FlG.  34.    The  outer  muscles  of  the  body. 
60 


THE  MUSCLES  6 1 

out  the  body.  They  number  more  than  five  hundred,  and 
more  than  two  fifths  of  the  entire  body  weight  is  muscle. 
The  lean  meat  of  animals  is  muscle,  and  by  examining  the 
body  of  an  animal  in  a  butcher  shpp,  you  can  see  that  a 
great  portion  of  the  entire  body  is  composed  of  muscles. 

The  Functions  of  Muscles.  The  first  and  cJiief  ftmction  of 
the  muscles  is  to  move  the  body.  The  muscles  cause  the  move- 
ments when  we  walk  or  run,  when  we  turn  the  head  or  eyes, 
when  we  swallow,  when  we  breathe,  or  when  the  heart  beats. 
The  body  cannot  move  in  any  way  except  by  means  of  the 
muscles. 

The  second  functiqp  of  the  muscles  is  to  help  the  bones  in- 
close the  body  cavities,  and  thus  protect  the  delicate  internal 
organs. 

The  third  function  of  the  muscles  is  to  assist  the  ligaments 
in  binding  the  skeleton  together  at  the  joints.  Nearly  every 
muscle  in  the  body  stretches  across  a  joint  and  is  attached 
on  each  side  of  it,  and  the  strong  muscles  are  a  great  aid  in 
holding  the  skeleton  together. 

How  the  Muscles  move  the  Body.  Muscle  cells  1  are  so 
long  that  they  are  often  spoken  of  as  muscle  fibers.  They 
have  the  power  of  contracting,  or  of  drawing  up  and  becoming 
shorter  and  thicker,  as  a  worm  does  in  crawling.  When  the 

1  The  cells  of  voluntary  and  involuntary  muscles  are  very  different  in  appear- 
ance. Involuntary  muscle  cells  (Fig.  5)  are  spindle-shaped,  and  are  several 
times  as  long  as  the  average  body  cell.  Voluntary  muscle  cells  (Fig.  35)  are 
slender  fibers  often  two  and  a  half  inches  long,  which  is  many  hundreds  of  times 
longer  than  an  ordinary  cell  (see  footnote  on  page  4).  An  involuntary  muscle 
cell,  like  an  ordinary  cell,  has  only  one  nucleus.  A  voluntary  muscle  cell  has 
thousands  of  nuclei.  The  reason  for  this  is  that  the  nucleus  is  the  part  of  the 
protoplasm  that  enables  the  cell  to  take  in  and  use  food,  and  one  nucleus  would 
not  be  enough  for  a  cell  containing  the  great  amount  of  protoplasm  found  in  a 
voluntary  muscle  cell. 


62 


HUMAN  PHYSIOLOGY 


BLOOD   VESSEL 


cells  in  a  muscle  contract,  the  whole  muscle  is  shortened. 
This  causes  a  bending  at  the  joint  over  which  the  muscle 
passes,  and  a  movement  of  some  part  of  the  body,  since 
the  muscle  pulls  on  the  bones  to  which  it  is  attached.  From 
Figure  39  you  can  understand  how,  when  the  biceps  muscle 
contracts,  the  arm  is  bent  at  the  elbow  and  the  hand  raised. 
Voluntary  and  Involuntary  Muscles.  Muscles  are  divided 
into  two  great  classes,  —  voluntary  and  involuntary  muscles. 
Voluntary  muscles  are  under  the  control  of  the  will.  They  are 
governed  by  the  brain,  and  we  can  contract  them  when  we 

wish.  Try  to  raise  your  hand 
and  you  can  do  so,  because  it 
is  moved  by  voluntary  muscles. 
Nearly  all  the  voluntary  mus- 
cles are  attached  to  the  skele- 
ton. 

Involuntary  muscles  are  not 
under  the  control  of  the  will. 
They  are  governed  by  the  sympa- 
thetic nervous  system,  and  over 
them  the  will  has  no  control.  If 
food  were  started  down  your 
throat,  you  would  be  compelled 
to  swallow  it  even  though  you 
knew  it  contained  poison,  for  the 
muscles  of  the  throat  are  invol- 
untary muscles.  The  involun- 
tary muscles  are  found  chiefly  in 
the  blood  vessels,  walls  of  the 
heart,  digestive  organs,  and  in 
other  internal  parts  of  the 
body. 


FIG.  35.  A  is  a  portion  of  a  muscle 
showing  the  connective  tissue  cover- 
ing (perimysium)  and  the  connec- 
tive tissue  partitions  which  divide 
the  muscles  into  bundles  of  muscle 
cells  (fasciculi).  In  B  a  part  of  a 
bundle  of  cells  is  shown  more  highly 
magnified.  The  length  of  the  mus- 
cle cells  is  so  great  that  only  a  small 
portion  of  any  one  cell  can  be  shown. 


THE  MUSCLES 


The  Connective  Tissue  Skeleton  of  Muscles.  The  muscles 
are  held  together  by  connective  tissue,  and  the  arrangement  of 
this  tissue  in  a  voluntary  muscle  is  very 
similar  to  its  arrangement  in  a  nerve. 
A  muscle  has  a  connective  tissue 
sheath,  which  covers  it  like  a  thin 
skin  (Fig.  35).  Connective  tissue 
partitions  l  run  in  from  the  sheath  all 
through  the  muscle,  dividing  the  mus- 
cle cells  into  groups  and  tying  them 
up  into  bundles.  Fine  fibers  of  con- 
nective tissue  are  woven  in  among  the 
individual  muscle  cells,  so  that  the 
muscle  has  around  it,  and  running  all 
through  it,  a  framework  of  connective 
tissue.2  The  connective  tissue  passes 
out  at  the  ends  of  a  muscle  and,  be- 
coming entangled  and  interwoven  with 
the  fibers  of  the  periosteum,  attaches 
the  muscle  to  the  skeleton  (Fig.  36). 

Tendons.  The  connective  tissue  may 
pass  directly  from  the  muscle  into  the 
periosteum  of  the  bone.  Often,  how- 
ever, the  connective  tissue  from  a  mus- 
cle unites  and  forms  a  tough  white 


1  In  a  piece  of  meat  cut  "  across  the  grain  "  (  i.e. 
across  the  muscle  cells)  the  connective  tissue  parti- 
tions in  the  muscle  may  easily  be  seen. 

2  Not  only  the  muscles,  but  the  whole  body  has 
a  complete  framework  of  connective  tissue.     If  all 
materials  of  the  body  except  the  connective  tissue 
were  removed,  there  would  still  remain  the  form 
of  the  whole  with  all  the  organs  in  place. 


FlG.  36.  Diagram  show- 
ing how  the  connective  tis- 
sue passes  through  a  muscle 
from  bone  to  bone.  The 
muscle  cells  are  shown 
many  times  larger  than  they 
would  actually  appear. 


64 


HUMAN  PHYSIOLOGY 


cord  called  a  tendon.  The  tendon  passes  to  a  bone  —  some- 
times to  a  bone  at  a  considerable  distance  from  the  muscle  — 
and  attaches  itself  to  the  bone  by  spread- 
ing out  on  its  surface  and  sending  its 
fibers  in  among  the  fibers  of  the  perios- 
teum. 

Uses  of  Tendons.  Certain  parts  of  the 
body  (the  hands,  for  example)  need  to 
have  great  strength  and  to  be  capable  of 
making  a  variety  of  movements,  without 
at  the  same  time  becoming  so  covered 
with  muscles  that  they  will  be  large  and 
heavy.  In  such  parts  of  the  body,  the 
muscles  are  placed  at  a  distance  and 
joined  to  the  bones  by  tendons.  There 
are  nearly  thirty  muscles  for  moving  the 
fingers  of  each  hand.  If  all  these  mus- 
cles were  on  the  hand,  it  would  not  be 
very  beautiful,  and  would  be  too  clumsy 
to  do  any  fine  work.  The  muscles  that 
move  the  fingers  are,  therefore,  placed 
on  the  forearm,  and  only  slender  tendons 
run  down  to  the  hand.  Open  and  close 
your  hand,  and  you  can  see  and  feel  the 
muscles  working  in  your  forearm,  and  in 
the  wrist  and  back  of  the  hand  you  can 
see  the  movements  of  the  tendons  which 
close  and  open  the  fingers. 

Tendons  held  in  Place  by  Ligaments. 
In  Figure  37  you  can  see  that  the  tendons 
pass  under  strong  ligaments  which  surround  the  wrist.  In 
many  other  parts  of  the  body  there  are  ligaments  forming 


FIG.  37.  The  muscles 
of  the  forearm  and  the 
tendons  and  ligaments  of 
the  hand  and  wrist. 


THE  MUSCLES 


bands  and  loops,  which  hold  the  tendons  down  close  to  the 
bones.  You  can  learn  the  necessity  for  these  ligaments  by 
an  experiment,  and  the  same  experiment  will  teach  you 
something  about  tendons. 

Tie  a  piece  of  string  about  the  tip  of  the  first  or  second  finger. 
Run  the  string  back  along  the  front  of  the  finger,  across  the  palm, 
and  up  the  wrist  to  the  forearm.  This  string  is  to  represent  a  tendon. 
Now  get  one  of  your  schoolmates  to  tie  strings  around  your  finger, 
hand,  and  wrist,  as  you  see  in  Figure  38.  These  strings  represent  the 
ligaments  which  hold  the  tendons  in  place.  From  up  on  the  fore- 
arm pull  on  the  cord  which  represents  the  tendon.  What  effect  has 
it  on  the  finger  and  hand?  Cut  the  cords  which  represent  the 
ligaments,  and  pull  on  the  cord  representing  the  tendon  as  before. 
Does  the  cord  follow  the  curves  of  the  fingers  and  hand,  and  lie 
down  flat  along  the  bones  ?  What  difficulty  would  we  have  in  the 
hand  if  the  tendons  were  not  tied  down  to  the  bones  ?  Now  turn 
the  string  about  and  run  it  down  the  back  of  the  finger  and  hand, 
and  note  how  a  tendon  pulling  on  the  back  of  the  finger  will  open  it. 

From  this  experiment  you  will  understand  the  use  of  the 
ligaments  in  the  hand  and  wrist;  you  will  also  realize  that 
without  the  ligaments  around  the 
ankles,  the  tendons  would  rise  and 
run  straight  from  the  toes  to  the 
muscles  below  the  knees ;  and  that 
all  through  the  body  it  is  very 
necessary  for  the  tendons  to  be  tied 
down  close  to  the  skeleton. 

Constant  Contraction  of  Muscles. 
Lay  the  back  of  your  hand  on  the 
desk,  stiffen  your  arm  at  the  elbow, 
and  bear  down  on  the  desk.     Now 
feel  the  muscle  on  the  back  of  your  FIG.  38.    illustrating  how  a  ten- 
upper  arm.     It  is  hard   and  con-  don  bends  a  finger' 
tracted.     It  is  keeping  your  arm  from  bending  by  pulling  on 


66 


HUMAN  PHYSIOLOGY 


the  point  of  the  ulna  at  the  elbow.  Now  stand  on  one  leg 
with  the  knee  of  that  leg  slightly  bent,  and  feel  the  muscles 
both  above  and  below  the  knee.  They  are  tightly  contracted 
because  they  are  holding  the  knee  and  ankle  joints  from 
giving  way  under  the  weight  of  the  body. 

You  know  that  if  a  man  goes  to  sleep 
when  sitting  up,  his  head  falls  forward. 
The  muscles  which  support  the  head  must 
keep  a  constant  contraction  to  hold  it  erect, 
and  when  the  man  goes  to  sleep  these 
muscles  relax.  A  dead  body  will  not  stand 
up,  but  will  give  way  at  the  joints.  The 
living  body  can  stand  up  because  the  mus- 
cles keep  the  body 
from  bending  at 
the  ankles,  knees, 
hips,  and  in  the 
back.  Not  only 
when  the  body 
moves,  but  when 
any  part  of  it  is 
held  erect  or  ex- 
tended, the  mus- 
cles must  be  con- 
tracted to  hold  it 
in  position.  Try  holding  the  arm  extended  for  five  minutes, 
or  standing  perfectly  still  for  some  time,  and  you  will  soon 
find  that  some  of  your  muscles  are  doing  heavy  work,  al- 
though there  is  no  movement  of  the  body. 

Antagonistic  Muscles.  Many  of  the  muscles  of  the  body 
are  in  pairs,  each  muscle  of  the  pair  working  against  the 
other.  Muscles  which  oppose  each  other  in  this  way  are 


FIG.  39. 


The  antagonistic  action  of  the  biceps  and 
triceps  muscles. 


THE  MUSCLES  67 

called  antagonistic  muscles.  An  excellent  example  of  a  pair 
of  antagonistic  muscles  is  found  in  the  upper  arm.  On  the 
front  is  the  biceps,  which  lifts  up  the  forearm.  On  the  back 
of  the  arm  is  the  triceps,  which  straightens  out  the  forearm. 
In  the  leg,  both  above  and  below  the  knee,  other  antagonistic 
muscles  will  be  found,  and  as  you  study  the  muscles  of  the 
body,  you  will  note  that  nearly  all  of  them  are  arranged 
to  work  in  opposition  to  other  muscles.  This  is  necessary, 
for  a  muscle  cannot  push,  and  if  a  part  of  the  body  is  to 
be  moved  back  and  forth,  it  must  have  a  muscle  to  pull  it 
each  way. 

Accuracy  of  Motion  given  by  Antagonistic  Muscles.  The 
antagonistic  action  of  muscles  is  very  important  in  giving  us 
control  of  our  movements.  Suppose  you  wish  to  extend  the 
forearm  to  pick  up  something.  You  do  this  by  contracting 
the  triceps.  If  there  were  no  biceps,  the  forearm  would  be 
thrown  out  with  a  jerk,  and  would  probably  go  beyond  the 
object  for  which  you  were  reaching.  But  as  the  muscles  are 
arranged,  the  biceps  exerts  a  steady,  even  pull  against  the 
triceps,  and  when  the  hand  has  been  extended  far  enough, 
the  biceps  gives  a  pull  strong  enough  to  balance  the  action 
of  the  triceps,  bringing  the  hand  to  a  stop  at  just  the  right 
place  to  grasp  the  object.  The  brakes  on  a  street  car  or  on 
a  railroad  train  make  it  possible  to  stop  at  the  desired  place. 
In  the  same  way,  the  antagonistic  action  of  the  muscles  en- 
ables us  to  check  the  movements  of  the  body  and  keep  them 
from  going  too  far. 

The  Nervous  Control  of  the  Muscles.  The  way  in  which 
the  nervous  system  controls  all  the  muscles  and  makes  them 
move  the  body  about,  seems  almost  as  wonderful  as  a  story 
from  the  Arabian  Nights.  You  look  at  a  book  and  wish  to 
read  in  it;  your  hand  reaches  out  and  grasps  the  book,  opens 


68  HUMAN  PHYSIOLOGY 

it  at  the  place  where  you  wish  to  read,  and  holds  it  up  before 
your  eyes.  You  wish  to  go  out  of  the  room;  your  body 
rises,  your  feet  carry  you  along,  and  out  of  the  room  you  go. 
You  wish  to  throw  a  ball  to  one  of  your  playmates;  the 
muscles  of  your  legs  and  back,  the  muscles  which  draw  back 
the  shoulder,  arm,  and  hand,  those  which  draw  these  parts 
forward  again,  and  the  muscles  which  open  the  hand  to  re- 
lease the  ball,  are  all  brought  into  action.  Each  one  of  this 
great  number  of  muscles  must  contract  at  exactly  the  right 
time,  with  exactly  the  right  force,  and  must  not  remain  con- 
tracted a  moment  too  long,  or  the  ball  will  go  wide  of  the 
mark,  and  you  will  make  a  poor  throw. 

All  such  movements  are  accomplished,  not  by  each  muscle 
working  independently,  but  only  through  the  nervous  system, 
which  controls  them  all.  From  the  brain  or  spinal  cord  a  nerve 
goes  to  every  voluntary  muscle  in  the  body,  and  a  branch  of 
a  nerve  fiber  goes  to  each  muscle  cell  (Fig.  102).  When 
you  wish  to  make  a  certain  movement,  the  commands  pass 
through  the  nerves  to  the  proper  muscles,  the  muscle  cells 
contract,  and  the  movement  is  made. 

The  voluntary  muscle  cells  are  controlled  by  the  central 
nervous  system.  Many  commands  are  sent  to  them  without 
our  thinking  about  it;  many  movements  have  been  made  by  us 
so  often  that  the  cord  and  brain  send  the  right  commands 
without  thought.  But  all  of  the  voluntary  muscles1  are  under 
the  control  of  the  will,  and  when  we  desire  to  do  so,  we  can 
send  a  message  from  the  brain  to  any  one  of  these  muscles 
and  make  it  contract. 

1  The  muscles  that  are  used  in  breathing  are  in  a  sense  intermediate  between 
the  voluntary  and  involuntary  muscles.  We  can  control  them  for  a  short  time; 
but  if  the  breath  is  held,  they  soon  act  in  spite  of  the  will.  Try  holding  your 
breath  and  you  will  find  that  it  is  possible  to  do  so  for  only  a  short  time. 


THE  MUSCLES 


69 


THE   CARRIAGE   OF  THE  BODY 

It  would  be  interesting  and  profitable1  to  locate  a  number 
of  the  more  prominent  muscles  of  the  body  and  to  study  their 
action,  but  we  have  time 
to  take  up  only  the  mus- 
cles that  support  the  spinal 
column.  From  your  study 
of  the  skeleton  you  already 
understand  that  the  entire 
upper  part  of  the  body 
stands  up  on  the  spinal 
column  as  on  a  stem  (Fig. 
19),  and  that  if  the  spinal 
column  droops,  the  head 
and  the  whole  framework 
of  the  chest  must  stoop 
forward.  It  is  therefore 
not  necessary  to  explain 
to  you  why  these  muscles 
are  so  important  from  the 
hygienic  standpoint. 

The  Long  Muscles  of  the 
Back.  Along  the  dorsal 
side  of  the  spinal  column 
are  long  muscles  for  supporting  the  spine  and  for  keeping 
the  skull  from  falling  forward.  The  muscles  of  the  back  are 
heaviest  in  the  lumbar  region  (the  "  small  of  the  back "), 

1  To  THE  TEACHER  :  If  time  will  permit,  some  exceedingly  valuable  work  may 
be  done  by  having  the  pupils  learn  the  origin,  insertion,  and  action  of  some  of 
the  muscles  shown  in  Figure  34.  The  most  interesting  and  profitable  part  of  the 
work  will  be  the  location  of  these  muscles  on  the  body. 


FIG.  40.    The  muscles  of  the  head. 


HUMAN  PHYSIOLOGY 


STERNOMASTOID 


where  the  two  large  erectors  of 'the 
spine  (erector  spinae)  may  easily  be 
felt  on  either  side  of  the  spinous 
processes  (Fig.  2 1 )  of  the  vertebrae. 
When  the  long  muscles  of  the 
back  contract  they  straighten  the 
upper  part  of  the  spinal  column, 
as  the  tendons  on  the  backs  of 
the  fingers  open  the  hand.  When 
the  muscles  of  the  back  are  weak 
they  allow  the  head  and  the  upper 
part  of  the  spine  to  droop  forward, 
spoiling  the  appearance  and  allow- 
ing the  framework  of  the  chest  to 
drop  down  and  crowd  the  lungs 
and  heart. 

The  Abdominal  Muscles.  The 
abdominal  muscles  are  long,  thin, 
flat  muscles  lying  in  the  abdominal 
walls.  These  muscles  connect  the 
ribs  and  sternum  with  the  rim  of 
the  pelvis  and  prevent  the  upper 
part  of  the  trunk  from  being 
drawn  over  backward  by  the  long 
muscles  of  the  back.  The  abdom- 
inal muscles  also  hold  the  internal 
organs  in  place,  and  by  forcing  the 

internal  organs  back  against  the  dorsal  wall  of  the  abdominal 

cavity,  support   the    spinal  column  in  front  in  the  lumbar 

region. 

The  Psoas  Muscles.     The  heavy  psoas  muscles  are  attached 

along  the  spinal  column  in  the  lumbar  region.     These  muscles 


FIG.  41.  The  muscles  that  sup- 
port the  spinal  column.  It  is  these 
muscles,  and  not  the  muscles  of  the 
shoulders,  that  hold  the  body  erect. 


THE  MUSCLES 


OBLIQUUS  ABDOMINIS 


ERECTOR   SPIN/E 


have  two  functions.  They  lift  the  thigh,  or  if  the  leg  is  held  so 
that  it  cannot  be  raised,  they  bend  the  body  forward  at  the  hips. 
They  also  brace  the  spinal  column  on  the  front  of  the  lumbar 
curve,  preventing  too  great  a  forward  curvature  at  this  point. 

How  to  acquire  and  keep  an  Erect  Carriage.  In  bringing 
the  body  to  an  erect  position,  the  great  thing  is  to  straighten 
out  the  curves  of  the  spi- 
nal column.  Straighten 
the  upper  curve,  and  the 
head  and  chest  will  be 
lifted.  Straighten  the 
lower  curve,  and  the  ab- 
domen will  be  drawn  in. 
Teach  the  muscles  on 
both  sides  of  the  spinal 
column  to  keep  the 
proper  contraction,  and 

the  body  will  Stand  erect.        FIG.  42.     A  diagram  of  a  cross-section  through 

The  easiest  wav  of  train-    ^e  ^um^ar  regi°n  °f  the  body.     The  erectors  of 

'  .       the  spine  (erector  spinae)  and  the  psoas  muscles 

ing  the  muscles  to  do  this    actjng  against  each  other  keep  the  spinal  column 

work  properly  is  to  stand  erect- 

and  walk  as  thougJi  yon  were  hung  by  the  top  of  the  head, 
a  little  back  of  the  center.  This  will  cause  the  spinal  column 
to  be  straightened  out,  pull  in  the  abdomen,  and  bring  up  the 
head  until  it  balances  on  top  of  the  spinal  column.  Stand  in 
this  position,  and  note  that  your  head  is  back  and  your  chin 
is  close  to  your  neck,  your  ribs  and  sternum  are  lifted  off  the 
heart  and  lungs,  and  the  muscles  are  tightened  across  the 
abdomen,  forcing  the  abdominal  organs  back  and  up.  "  Stand 
tall"  thrusting  up  the  top  of  the  head  as  high  as  possible,  and 
drawing  the  chin  and  abdomen  in,  is  the  best  rule  for  position 
in  standing  and  walking. 


72  HUMAN  PHYSIOLOGY 

Mistakes  made  in  trying  to  stand  Erect.  The  most  com- 
mon of  all  mistakes  made  in  trying  to  acquire  a  good  carriage 
is  to  try  to  hold  the  body  erect  by  forcing  back  the  shoulders. 
Contracting  the  trapezius  muscles  (Fig.  34)  and  drawing  the 
scapulas  back  toward  the  middle  of  the  back,  or  pulling  the 
shoulders  back  with  braces,  will  never  bring  the  body  to  an 
erect  position.1  The  true  remedy  is  to  straighten  out  the 
spinal  column.  The  shoulders  will  take  care  of  themselves  if 
only  a  little  care  is  used  to  see  that  they  are  not  lifted  too 
high  when  the  body  is  straightened  up. 

The  other  common  mistake  made  in  trying  to  stand  erect 
is  to  throw  the  head  and  chest  up  and  allow  the  abdomen  to 
be  thrust  forward.  The  trouble  is  that  although  the  muscles 
along  the  back  are  contracted,  bringing  up  the  upper  part  of 
the  spine,  yet  the  psoas  and  abdominal  muscles  are  allowed 
to  relax,  and  the  spinal  column  bends  inward  in  the  lumbar 
region. 

Importance  of  acquiring  a  Correct  Carriage  in  Youth.  If 
the  body  is  not  held  erect  in  youth  the  bones  will  harden  in  a 
stooping  position,  the  cartilages  between  the  vertebrae  will 
become  wedge-shaped,  and  the  muscles  will  develop  in  length 
to  fit  a  stooped  skeleton  instead  of  a  straight  one.  Youth 
is  also  the  best  time  to  build  up  and  strengthen  weak  mus- 
cles, and  to  teach  all  the  muscles  to  keep  a  proper  amount  of 
contraction. 

The  easiest  way  to  acquire  an  upright  carriage  is  to  form 
the  habit  of  sitting,  standing,  and  walking  erect.  "  Stand 
tall,"  and  the  muscles  will  fall  into  the  habit  of  keeping  the 
spinal  column  upright.  It  is  possible,  however,  by  suitable 

1  "The  position  of  the  shoulders  has  hardly  any  effect  upon  the  position  of  the 
body.  They  hang  upon  the  outside  of  the  body  like  the  blinds  on  a  house." 
—  DR.  LUTHER  H.  GULICK. 


THE  MUSCLES  73 

exercise,  to  develop  and  strengthen  weak  muscles,  and  if  you 
are  inclined  to  stoop  you  should  exercise  especially  the  mus- 
cles that  support  the  spine. 


HYGIENE   OF  MUSCLES 

All  the  cells  of  the  body  live  together,  and  it  is  not  possible 
to  have  some  of  them  in  bad  condition  and  the  remainder  of 
them  in  good  health.  Whatever  keeps  the  whole  body  in 
health,  therefore,  benefits  the  muscles.  Among  these  things 
are  plenty  of  good  food,  fresh  air,  and  sleep.  Other  things 
that  are  necessary,  not  only  for  the  health  of  the  muscles  but 
for  the  health  of  the  whole  body,  are  exercise  and  rest. 

Importance  of  Exercise.  Exercise  benefits  the  body  in 
many  ways.  It  quickens  the  breathing  and  starts  the  heart 
to  beating  faster,  and  it  stirs  up  the  different  organs  of  the 
body  and  causes  more  blood  to  flow  through  them.  Without 
exercise  the  muscles  become  weak  and  soft,  and  it  is  also  true 
that  if  the  muscles  are  not  exercised  the  whole  body,  espe- 
cially the  digestive  organs,  will  get  out  of  order.  A  whole 
book  could  be  written  on  this  subject,  but  any  one  who 
wishes  to  take  healthful  exercise  knows  how  to  do  so,  and 
we  will  merely  call  your  attention  to  the  following  important 
facts: 

The  muscles  should  be  exercised  every  day.  Any  one  who 
is  lazy  and  neglects  to  do  this  will  surely  suffer,  for  without 
exercise  the  body  cannot  keep  in  health.  Exercise  should  be 
stopped  before  one  becomes  too  tired,  for  too  much  exercise  is 
worse  than  not  enough.  Whenever  possible -,  exercise  should  be 
taken  outdoors.  Outdoor  games  furnish  enjoyment,  fresh  air, 
and  exercise  all  at  the  same  time  and  are  the  best  of  all  forms 
of  exercise. 


74  HUMAN  PHYSIOLOGY 

Effects  of  Tobacco  and  Alcohol  on  the  Muscles.  Tobacco, 
so  far  as  we  know,  is  injurious  to  all  of  the  body  cells. 
Certainly  it  weakens  the  muscles.  Athletes  who  wish  to  have 
their  muscles  in  such  condition  that  they  will  contract  with  the 
greatest  possible  power,  are  not  allowed  to  use  tobacco. 

Alcohol  also  weakens  the  muscles,  especially  in  any  long- 
continued  effort.  Shrewd  old  Benjamin  Franklin  knew  this 
long  ago.  In  speaking  of  the  time  when  he  worked  in  a 
London  printing  house,  he  says  :  "  I  drank  only  water.  The 
other  workmen,  fifteen  in  number,  were  great  drinkers  of  beer. 
On  occasions  I  carried  up  and  down  stairs  a  large  form  of 
types  in  each  hand,  when  others  carried  but  one  in  both 
hands.  They  wondered  to  see  from  this  and  several  in- 
stances, that  the  Water-American,  as  they  called  me,  was 
stronger  than  themselves,  who  drank  strong  beer." 

Arctic  explorers  have  found  that  they  fared  best  when  they 
used  no  alcohol.  In  mountain  climbing,  in  the  cold  air  of  the 
high  Alps,  it  has  been  found  by  experiment  that  a  man  could 
do  20  per  cent  more  work  on  days  when  he  used  no  alco- 
hol than  the  same  man  could  do  on  days  when  a  moderate 
amount  of  alcohol  was  used.  In  the  hot  climates  of  Africa 
and  India  it  has  been  found  that  regiments  of  soldiers  with- 
out alcohol  can  outmarch  those  using  it.  Thus  in  both  cold 
and  heat,  alcohol  users  have  less  endurance  than  those  who 
do  not  use  it.  Both  alcohol  and  tobacco  weaken  the  muscles, 
and  they  do  this  chiefly  by  injuring  the  nervous  system, 
which  controls  the  muscles. 

Summary.  The  muscles  number  more  than  five  hundred 
and  make  up  more  than  two  fifths  of  the  body  weight.  They 
move  the  body,  help  inclose  the  body  cavities,  and  assist  in 
binding  the  skeleton  together.  The  two  classes  of  muscles 
are  the  voluntary  and  involuntary. 


THE  MUSCLES  75 

A  muscle  has  a  framework  of  connective  tissue  by  which 
it  is  attached  to  the  skeleton.  In  some  cases  the  connective 
tissue  forms  a  tendon  and  runs  to  a  bone  at  a  distance  from 
the  muscle.  The  tendons  are  held  down  close  to  the  skele- 
ton by  ligaments. 

The  muscles  of  the  body  keep  a  certain  amount  of  contrac- 
tion, as  is  shown  by  the  fact  that  a  dead  body  will  not  stand 
up.  Most  of  the  muscles  are  arranged  in  pairs,  one  muscle 
of  the  pair  working  in  opposition  to  the  other.  The  nervous 
system  controls  the  muscles  and  causes  them  to  work  together 
in  a  wonderful  manner. 

In  the  carriage  of  the  body,  the  muscles  of  the  spinal 
column  are  the  ones  that  are  important.  The  erectors  of  the 
spine,  the  abdominal  muscles,  and  the  psoas  muscles  support 
the  spinal  column  and  should  be  taught  to  keep  a  proper 
amount  of  contraction.  The  best  way  to  do  this  is  to  form 
the  habit  of  standing  and  walking  erect. 

A  common  mistake  in  trying  to  acquire  an  erect  carriage 
is  to  pull  the  shoulders  back  instead  of  straightening  up  the 
spinal  column.  Another  mistake  is  to  allow  the  spinal  column 
to  bend  forward  too  much  in  the  lumbar  region.  In  youth 
is  the  time  to  acquire  a  good  carriage. 

Exercise  is  necessary,  not  only  for  the  health  of  the  mus- 
cles, but  for  the  health  of  the  other  organs  of  the  body  as 
well.  Tobacco  and  alcohol  weaken  the  muscles  and  should 
not  be  used  by  those  who  wish  to  be  strong. 

QUESTIONS 

How  many  muscles  are  in  the  body?  How  much  of  the  body 
weight  is  muscle? 

Give  three  functions  of  the  muscles.  What  causes  a  muscle  to 
contract?  Explain  how  the  biceps  muscle  bends  the  arm.  Name 


76  HUMAN  PHYSIOLOGY 

the  two  classes  of  muscles.  What  is  the  difference  between  them? 
To  what  are  the  voluntary  muscles  attached?  Where  are  the  invol- 
untary muscles  found? 

Describe  the  connective  tissue  skeleton  of  a  muscle.  How  is  a 
muscle  attached  to  a  bone  ?  Of  what  is  a  tendon  composed  ?  What 
advantage  is  there  in  having  tendons  in  the  body?  How  are  the 
tendons  kept  close  to  the  bones? 

Why  does  a  man's  head  remain  erect  when  he  is  awake  and  fall 
forward  when  he  goes  to  sleep?  What  are  antagonistic  muscles? 
Give  an  example.  Why  are  the  muscles  of  the  body  arranged  in 
pairs?  What  effect  have  the  antagonistic  muscles  on  our  movements? 

What  has  the  nervous  system  to  do  with  our  movements?  By 
what  part  of  the  nervous  system  are  the  voluntary  muscles  controlled  ? 
Where  are  some  of  the  muscles  that  are  used  in  walking?  Do  you 
think  of  the  movements  caused  by  all  these  muscles? 

What  part  of  the  skeleton  supports  the  head  and  trunk?  What 
muscles  keep  the  upper  part  of  the  spinal  column  erect  ?  What  fol- 
lows if  these  muscles  are  weak  or  relaxed  too  much?  Give  two 
functions  of  the  abdominal  muscles ;  two  functions  of  the  psoas 
muscles.  If  these  muscles  are  weak  or  relaxed,  what  effect  has  it  on 
the  curves  of  the  spinal  column?  What  is  the  best  method  of  train- 
ing the  muscles  to  hold  the  spinal  column  erect?  Give  the  rule  for 
position  in  standing  and  walking.  What  two  mistakes  are  often  made 
in  trying  to  stand  erect?  Why  is  it  important  to  acquire  a  correct 
carriage  in  youth  ? 

Name  four  things  necessary  to  the  health  of  the  body.  Mention 
some  of  the  effects  of  exercise  on  the  body.  What  effect  has  lack  of 
exercise  on  the  muscles?  on  the  other  organs  of  the  body?  What 
three  important  statements  are  made  in  regard  to  exercise  ? 

What  effect  has  tobacco  on  the  muscles?  Tell  of  Franklin's  expe- 
rience in  the  London  printing  house.  What  effect  had  alcohol  on  the 
power  of  a  man  to  work  in  the  cold  air  of  the  Alps  Mountains  ?  What 
effect  has  it  on  the  endurance  of  men  in  hot  climates  ?  In  what  way 
do  alcohol  and  tobacco  chiefly  affect  the  muscles? 


THE  MUSCLES  77 

REVIEW   QUESTIONS 

Chapter  I.  Of  what  are  living  things  composed?  How  do  cells 
originate  ?  Why  is  it  necessary  that  there  should  be  a  division  of 
labor  among  the  cells  of  the  body?  Name  some  of  the  different 
kinds  of  cells  in  the  body  and  give  their  functions. 

Define  :  protoplasm  ;  nucleus ;  tissue  ;  organ  ;  anatomy  ;  physi- 
ology ;  hygiene. 

Chapter  II.  Name  and  locate  the  two  body  cavities.  What  is  in 
each?  Where  does  man  belong  in  the  animal  kingdom?  Mention 
some  ways  in  which  the  bodies  of  all  vertebrates  are  alike.  How 
does  the  human  body  differ  from  the  bodies  of  all  other  animals? 

Chapter  III.  What  is  the  function  of  the  nervous  system  ?  Explain 
why  some  such  system  is  necessary  in  the  body.  Name  the  divisions 
of  the  brain.  Describe  a  nerve.  What  is  the  function  of  the  nerves  ? 

Define  and  give  the  function  of  the  following :  central  nervous 
system  ;  sympathetic ;  dura  mater ;  arachnoid  ;  pia  mater ;  cerebro- 
spinal  fluid. 

Chapter  IV.  Give  three  functions  of  the  skeleton.  What  part  of 
the  skeleton  forms  a  central  axis  to  which  all  the  other  parts  are 
joined?  Name  bones  of  different  shapes  with  their  functions.  What 
materials  are  in  bones,  and  what  is  the  function  of  each  kind  of 
material?  What  advantage  is  there  in  the  hollow  structure  of  bones? 

Define  :    compact ;  spongy  ;  marrow ;  periosteum. 

Chapter  V.  Name  two  classes  of  joints ;  three  kinds  of  movable 
joints.  Describe  cartilage  and  tell  where  it  is  found.  How  is 
friction  kept  down  in  the  joints?  What  are  ligaments?  How  is 
the  skeleton  made  springy?  How  does  the  human  skeleton  resemble 
other  vertebrate  skeletons?  How  does  it  differ  from  the  skeleton  of 
an  ape?  Mention  some  points  in  connection  with  the  hygiene  of 
the  human  skeleton.  How  would  you  treat  a  broken  bone?  a 
dislocation?  a  sprain? 

Chapter  VI.  Give  the  functions  of  the  muscles.  How  are  muscles 
attached  to  bones?  Explain  how  the  muscles  move  the  body.  What 
muscles  are  important  in  the  carriage  of  the  body?  How  may  an 
erect  carriage  be  acquired?  What  mistakes  are  made  in  trying  to 
stand  erect  ?  Why  should  the  body  be  carried  erect  in  youth?  Speak 
of  the  importance  of  exercising  the  muscles  ;  of  the  effects  of  tobacco 
on  the  muscles ;  of  the  effects  of  alcohol  on  the  muscles. 


CHAPTER  VII 

FOODS   AND  ENERGY 

TO-DAY  we  take  in  food.  To-morrow  the  food  is  gone  and 
we  are  hungry  still.  We  eat  again  and  the  next  day  find  our 
need  for  food  as  great  as  it  was  at  first.  We  spend  our  lives 
working  for  food  and  eating  food,  and  yet  only  a  few  short 
hours  behind,  hunger  is  always  following  on  our  trail. 

Why  can  we  not  forget  all  about  food  ?  What  makes  us 
want  to  eat  ?  Why  do  we  spend  our  money  for  something 
that  we  cannot  keep  ?  Why  not  give  up  eating  and  have  time 
to  rest  and  enjoy  life?  Because  without  food  the  life  of  the 
cells  and  of  the  body  comes  to  an  end. 

Why  the  Cells  need  Food.  The  living  protoplasm  in  the 
cells  is  continually  wasting  away.  In  certain  parts  of  the 
body  the  cells  are  constantly  dying1  and  being  replaced  by 
new  cells.  Other  new  cells  are  needed  when  the  body  grows 
in  size  (page  10).  New  protoplasm,  therefore,  is  constantly 
being  built  up  for  the  repair  and  growth  of  the  cells,  and 
this  protoplasm  is  formed  from  the  materials  that  are  in  the 
foods.  Food  is  necessary  to  furnish  material  for  the  repair 
and  growth  of  the  cells. 

The  cells  get  their  energy  —  their  warmth  and  power  to 
work  —  from  the  food.  A  muscle  cell  gets  its  strength,  a 

1  It  is  estimated  that  fourteen  billion  red  blood  corpuscles  die  in  the  body  every 
day.  Great  numbers  of  cells  also  die  on  the  surface  of  the  skin. 

78 


FOODS  AND  ENERGY  79 

bone  cell  gets  its  power  to  build  bone,  and  all  other  cells, 
whatever  they  do,  get  their  power  to  work  from  the  energy 
which  is  in  the  food.  Just  as  a  locomotive  gets  its  energy  — 
its  warmth  and  power  to  move — from  the  fuel  which  is  burned 
under  its  boiler,  so  the  cell  gets  its  energy  from  the  food 
which  is  burned  within  the  cell.  Cut  off  the  fuel  from  a 
locomotive,  and  it  will  become  cold  and  still.  Cut  off  the 
food  from  a  cell,  and  it  will  lose  its  energy  and  become  a  dead 
cell.  Food  is  necessary  to  furnish  energy  to  the  cells. 


THE  CHEMISTRY  OF  FOODS 

Molecules  and  Atoms.  In  the  study  of  chemistry  we  learn 
that  everything  that  we  can  see,  feel,  taste,  or  smell  is  com- 
posed of  very  small  parts  called  molecules.  Just  as  a  house 
is  built  of  bricks,  so  are  wood,  stone,  water,  earth,  air,  and 
other  substances  composed  of  molecules. 

Molecules  are  so  small  that  millions  of  them  are  required 
to  build  the  smallest  object  that  can  be  seen  with  the  most 
powerful  microscope.  They  are  so  small  that  we  cannot 
imagine  how  small  they  are.  Yet  chemists  study  molecules, 
and  they  have  discovered  some  very  wonderful  things  about 
them.  One  of  the  most  wonderful  of  these  discoveries  is 
that  molecules  are  composed  of  still  smaller  particles  called 
atoms.  There  are  about  eighty  kinds  of  atoms,  all  differing 
in  many  ways. 

Elements  and  Compounds.  Elements  are  substances  that 
have  only  one  kind  of  atoms  in  their  molecules.  Compounds 
have  two  or  more  different  kinds  of  atoms  in  their  molecules. 
Perhaps  you  do  not  understand  what  you  have  just  read,  but 
if  we  play  that  we  are  building  molecules,  you  will  probably 


80  HUMAN  PHYSIOLOGY 

get  a  clear  idea  of  the  difference  between  an  element  and 
a  compound. 

Suppose  we  have  a  pile  of  bricks  of  many  different  colors, 
—  some  purple,  some  red,  some  yellow,  some  green,  some 
blue,  and  some  violet.  Suppose  we  call  these  bricks  atoms, 
and  of  them  decide  to  build  molecules.  Let  us  first  build 
a  molecule  using  only  red  bricks.  This  is  like  the  molecule 
of  an  element,  for  it  has  only  one  kind  of  atoms  in  it.  Let  us 
now  build  a  molecule  of  yellow  bricks.  This  also  is  like  the 
molecule  of  an  element,  for  only  one  kind  of  atoms  was  used 
in  making  it.  Now  let  us  build  a  molecule  partly  of  yellow 
and  partly  of  red  bricks.  Is  this  like  the  molecule  of  an 
element  ?  No,  for  it  has  in  it  two  kinds  of  atoms.  It  is  like 
the  molecule  of  a  compound.  Let  us  now  build  a  big  mole- 
cule and  put  into  it  all  the  different  kinds  of  bricks  that 
we  have.  Is  this  big  molecule  an  element  or  a  compound  ? 
Read  the  definition  of  a  compound  again,  and  you  will  see 
that  this  is  certainly  a  compound. 

Some  Common  Elements  and  Compounds.     Since  there  are 
eighty  kinds  of  atoms,  there  are  about  eighty  elements.     You 
could  tell  that  iron  is  an  element  from 
the  diagram  of  its  molecule,  for  both 
atoms  are  of  the  same  kind.     Gold  is 

FIG.  43.  A  molecule  of  iron,  another  element,  the  atoms  in  its  mole- 
Iron  is  an  element  because  all  cule  being  the  same.  Other  common 
the  atoms  in  its  molecule  are  eiements  are  silver,  copper,  lead,  tin, 

of  the  same  kind.  .  7/11111 

zinc,  sulfur,  and  carbon  (the  black  sub- 
stance of  which  charcoal  and  soot  are  composed,  and  which 
you  see  on  the  burnt  end  of  a  match).  Still  other  elements  are 
oxygen,  the  gas  which  is  taken  into  the  blood  from  the  air  when 
we  breathe;  hydrogen,  a  very  light  gas  used  to  fill  balloons; 
and  nitrogen,  a  gas  making  up  about  four  fifths  of  the  air. 


FOODS  AND  ENERGY  8 1 

Since  the  eighty  different  kinds  of  elements  combine  in 
very  many  different  ways,  there  are  thousands  of  compounds 
all  about  us.    Wood,  stone,  water, 
and    earth    are    all    compounds. 
Rocks  and  the  ores  of  metals  are 
compounds.     Dynamite  and  gun- 

FlG.   44.       A   molecule   of  water. 

powder    are    compounds    whose  Water  is  a  compound  because  it  has 

molecules  fly  to  pieces  with  great    more  than  one  kind  of  atoms  in  its 

force.      Everything  that  you  eat  molecule- 
and  wear  is  a  compound,  and  if  you  should  pick  up  the  thing 
nearest  your  hand,  you  would  probably  find  that  you  were 
holding  a  compound. 

Compounds  Different  from  the  Elements  of  which  they  are 
formed.  When  blue  and  yellow  paint  are  stirred  together, 
the  mixture  is  neither  blue  nor  yellow,  but  green.  So  a  com- 
pound may  be  very  different  from  any  of  the  elements  of 
which  it  is  formed.  Thus  when  carbon  (a  black  solid)  and 
sulfur  (a  yellow  solid)  unite,  they  make  a  liquid.  When  oxy- 
gen and  iron  unite,  they  make  the  red  rust  which  you  have 
so  often  seen.  This  rust  is  not  a  gas  like  oxygen,  nor  is  it  a 
tough  and  hard  metal  like  iron.  It  is  a  compound,  and  very 
different  from  each  of  the  elements  (oxygen  and  iron)  of 
which  it  is  made. 

Water  is  another  compound  which  is  different  from  either 

of  the  elements  in  it.     Hydrogen 
and  oxygen  are  both  gases,  but 
when  they  unite,  they  form  water, 
FiG74s.    A  molecule  ofTarbon  a  liquid.    Carbon  and  oxygen  also 
dioxid.   This  gas  is  a  compound,  its  form    a  compound   very   unlike 
molecules  having  in  them  two  kinds  dther  of   the  elements  entering 

into  it.      A  piece  of  charcoal  is 
a  black  solid  which  you  can  see  and  handle,  and  oxygen  is 


82  HUMAN  PHYSIOLOGY 

the  gas  of  the  air  which  is  so  necessary  to  our  lives.  But 
when  carbon  and  oxygen  unite  (as  they  do  when  you  burn  a 
piece  of  charcoal)  the  compound,  carbon  dioxid,  is  a  poisonous 
gas  very  different  from  the  solid  carbon,  and  also  very 
different  from  the  life-supporting  oxygen. 

Thdanguage  of  Chemists.     Chemists  do  not  write  out  the 

^ 

whole  names  of  the  elements,  but  write  H  for  hydrogen,  O 
for  oxygen,  S  for  sulfur,  C  for  carbon,  and  other  short  signs 
for  the  other  elements.  They  have  also  a  short  way  of  writ- 
ing out  the  kinds  of  atoms  and  how  many  of  each  kind  are  in 
a  compound.  Thus  they  write  H2O  (read :  H  two  O)  for 
water,  meaning  that  in  a  molecule  of  water  there  are  two 
atoms  of  hydrogen  and  one  atom  of  oxygen.  For  carbon 
dioxid,  the  poisonous  gas  which  we  breathe  out  from  the 
lungs,  and  which  is  formed  when  anything  containing  carbon 
is  burned,  they  write  CO2  (read :  CO  two),  meaning  that  in  a 
molecule  of  this  gas  there  are  one  atom  of  carbon  and  two  of 
oxygen. 

CLASSES   OF  FOOD 

From  plants  and  animals  the  people  of  the  world  obtain 
many  different  foods.  All  these  foods,  however,  can  be  put 
into  three  great  classes,  —  the  carbohydrates,  fats,  z.n.&  proteids. 

Carbohydrates.  The  carbohydrates  include  the  starches 
and  sugars.  Almost  all  of  them  come  from  plants.  Nearly 
every  plant  has  its  own  kind  of  starch,  and  we  have  corn 
starch,  wheat  starch,  oat  starch,  potato  starch,  arrowroot 
starch,  and  many  other  varieties  of  starch.  All  the  grains, 
potatoes,  and  most  vegetables  are  starchy  foods. 

Sugar  is  an  important  food.  Most  of  the  sugar  that  we 
use  comes  from  sugar  cane  and  the  sugar  beet.  Besides  what 


FOODS  AND  ENERGY  83 

we  purposely  add  to  our  foods  to  make  them  pleasant  to  the 
taste,  we  get  considerable  amounts  of  sugar  in  maple  syrup, 
molasses,  honey,  and  fruits,  and  there  is  some  sugar  in  corn, 
sweet  potatoes,  milk,  and  many  other  foods. 

Fats.  There  is  no  difference  between  fats  and  oils,  except 
that  at  ordinary  temperatures  fats  are  solid  and  oils  are 
liquid.  For  use  as  food  they  are  the  same,  and  are  all  called 
fatty  foods. 

Among  the  common  fatty  foods  are  butter,  taken  from 
milk ;  lard  and  cotton-seed  oil,  used  in  cooking ;  olive  oil,  used 
in  salads  and  dressings ;  and  the  fat  that  is  always  found  in 
meat.  Besides  the  fats  obtained  from  these  foods  we  get 
some  fats  in  eggs,  cheese,  corn,  chocolate,  and  in  a  great 
many  other  foods. 

Proteids.  Most  of  the  food  that  we  get  from  animals  con- 
tains proteids.  Lean  meat,  fish,  eggs,  milk,  and  cheese,  all 
contain  proteid  matter.  Corn  and  all  the  cereal  grains  except 
rice  contain  considerable  proteid  matter ;  but  of  all  common 
foods  obtained  from  plants,  peas  and  beans  are  the  richest  in 
proteids.  The  table  in  the  back  of  the  book  shows  the  pro- 
portion of  proteids,  carbohydrates,  and  fats  in  many  foods. 

Chemical  Composition  of  the  Different  Classes  of  Foods. 
The  carbohydrates  contain  the  three  elements,  carbon, 
hydrogen,  and  oxygen,  —  and  in  the  common  carbohydrates, 
as  in  water,  there  are  always  twice  as  many  atoms  of  hydro- 
gen as  there  are  atoms  of  oxygen.  Thus,  common  sugar  is 
C12H22On,  there  being  two  atoms  of  hydrogen  for  one  of  oxy- 
gen. Fats  contain  the  same  elements  as  the  starches  and 
sugars,  but  in  different  proportions,  having  in  them  much 
less  oxygen  than  is  found  in  the  carbohydrates.  Proteids 
contain  all  the  elements  (carbon,  hydrogen,  and  oxygen) 
which  are  found  in  the  other  foods,  and  in  addition  they 


84  HUMAN  PHYSIOLOGY 

contain  nitrogen  and  usually  very  small  amounts  of  sulfur, 
phosphorus,  iron,  and  other  elements. 

All  Foods  come  from  Living  Things.  From  what  you  have 
already  learned  you  will  know  that  the  principal  elements  in 
food  are  very  abundant  in  the  world.  Oxygen  and  nitrogen 
make  up  nearly  all  of  the  air.  Water  is  two  thirds  hydrogen, 
as  you  could  tell  by  counting  the  number  and  kinds  of  atoms 
in  its  molecules.  Carbon  is  abundant  in  wood  ;  coal  is  nearly 
all  carbon ;  and  there  is  much  carbon  in  the  rocks  of  the 
earth. 

But  you  could  not  live  on  water,  coal,  and  air.  They  con- 
tain all  the  chief  elements  of  our  food,  but  it  is  only  when 
these  elements  have  been  built  up  into  the  proper  compounds  ' 
that  they  are  useful  in  nourishing  the  body.  These  com- 
pounds we  find  only  in  the  bodies  of  living  things,  so  all  our 
food  must  come  from  the  bodies  of  animals  or  from  plants. 
"  In  building  our  house,  we  can  use  only  bricks  ripped 
from  the  walls  of  other  houses." 

Uses  of  the  Different  Classes  of  Foods.  Protoplasm  is  living 
proteid  matter ;  it  is  always  partially  composed  of  nitrogen, 
and  any  food  which  is  used  in  cell  building  must  contain 
nitrogen.  The  proteids  are  therefore  the  building  foods. 
The  fats  and  carbohydrates  lack  the  necessary  nitrogen,  and 
cannot  be  used  in  cell  building.  They  are  fuel  foods ,  tiseful 
for  burning  in  the  cells  to  furnish  energy.  The  proteids  when 
burned  also  furnish  energy  to  the  cells,  but  their  main  use 
is  to  provide  materials  for  building  new  protoplasm. 

OTHER  THINGS  NECESSARY  TO  THE  BODY 

Oxygen  and  Water.  Besides  the  three  classes  of  foods  that 
we  have  studied,  there  are  certain  other  substances  which  the 


FOODS  AND   ENERGY  85 

body  must  have  to  keep  it  in  health.  Among  these  things 
oxygen  takes  the  first  place.  We  breathe  it  in  constantly, 
and  if  the  supply  of  oxygen  is  cut  off  for  even  a  short  time, 
we  die.  Water  is  also  absolutely  necessary  to  the  body. 
Besides  the  water  that  we  drink,  we  get  a  great  deal  of  water 
in  our  foods,  as  you  can  see  by  referring  to  the  table  of  foods 
in  the  back  of  the  book.  Potatoes  are  more  than  80  per 
cent  water ;  beef  is  more  than  half  water ;  and  even  in  dry 
foods  like  rice  and  beans  there  is  water. 

Minerals.  Several  minerals  are  needed  by  the  body.  Of 
these  salt  is  needed  in  the  greatest  quantity.  During  the 
time  of  growth  the  body  must  have  also  a  considerable  quantity 
of  lime  to  build  the  skeleton.  Iron  in  small  amounts  is 
necessary  for  the  formation  of  the  red  blood  corpuscles,  and 
small  amounts  of  several  other  minerals  are  needed  by  the 
body.  Some  of  these  minerals  we  get  in  water,  and  others  in 
our  food.  The  green  parts  of  vegetables  have  a  special  value 
because  of  the  iron  they  furnish  to  the  red  corpuscles  of  the 
blood. 

Summary.  The  human  body  constantly  requires  food. 
This  food  is  necessary  to  furnish  building  material  and 
energy  to  the  cells. 

All  matter  is  composed  of  molecules  that  are  built  of  still 
smaller  particles  called  atoms.  Elements  have  only  one  kind 
of  atoms  in  their  molecules.  Compounds  have  two  or  more 
kinds  of  atoms  in  their  molecules.  There  are  about  eighty 
elements  and  thousands  of  compounds.  Compounds  are 
often  very  different  from  any  of  the  elements  of  which  they 
are  formed. 

The  three  classes  of  foods  are  the  carbohydrates  (starches 
and  sugars),  the  fats,  and  the  proteids.  The  carbohydrates 
are  obtained  chiefly  from  plants.  They  contain  carbon, 


86  HUMAN  PHYSIOLOGY 

hydrogen,  and  oxygen,  there  being  in  them  two  atoms  of 
hydrogen  for  each  atom  of  oxygen.  Fats  and  oils  contain 
these  same  elements  but  in  different  proportions.  Proteids, 
in  addition  to  the  elements  found  in  the  other  foods,  contain 
nitrogen.  Lean  meats,  eggs,  milk  and  cheese,  grains,  and 
peas  and  beans  are  the  principal  proteid  foods. 

The  elements  found  in  foods  are  very  abundant  in  the 
world,  but  only  compounds  built  up  by  living  plants  and 
animals  can  be  used  by  man  for  food.  The  proteids  give 
energy  to  the  body,  and  they  are  the  only  foods  that  can  be 
used  in  building  protoplasm,  because  only  the  proteids  con- 
tain nitrogen.  The  other  foods  furnish  energy  to  the  body. 

Oxygen,  water,  and  certain  minerals  are  also  necessary  to 
the  body.  The  body  obtains  its  minerals  from  water  and 
foods.  Green  vegetables  are  especially  valuable  for  their 
iron. 

QUESTIONS 

VGive  two  reasons  why  the  body  needs  food.  Why  do  the  cells 
need  building  material  ?  Why  do  they  need  energy  ? 

Of  what  is  all  matter  composed  ?  Of  what  are  molecules  com- 
posed? What  is  an  element?  What  is  a  compound?  Name  some 
elements ;  some  compounds.  Name  some  compounds  that  are 
different  from  the  elements  of  which  they  are  composed.  Give 
some  examples  of  the  short  signs  that  chemists  use. 

What  are  the  three  classes  of  foods?  What  two  kinds  of  carbo- 
hydrates are  there?  From  what  are  they  obtained?  Mention  some 
starchy  foods ;  some  foods  that  contain  sugar.  What  is  the  differ- 
ence between  a  fat  and  an  oil  ?  Mention  some  fatty  foods.  Mention 
a  number  of  foods  that  are  rich  in  proteids. 

What  elements  are  in  carbohydrates?  In  what  proportion  are  the 
hydrogen  and  oxygen  in  them?  What  elements  are  in  fats?  Give 


FOODS  AND  ENERGY  87 

two  uses  of  the  proteids  in  the  body.  How  are  the  carbohydrates 
and  fats  used  in  the  body?  From  what  kind  of  objects  are  our  foods 
obtained  ? 

Mention  some  other  things  that  are  needed  by  the  body.  Vwhere 
does  the  body  obtain  its  oxygen?  water?  mineral  matter?  What 
mineral  is  especially  found  in  the  green  parts  of  vegetables  ? 


When  gas  or  oil  is  burned,  what  becomes  of  the  atoms  of  which 
its  molecules  were  composed? 


CHAPTER  VIII 


THE   DIGESTIVE   ORGANS 

WE  have  now  learned  that  the  cells  of  our  bodies  must 
have  food.     But   before   one  of   the  cells  in  the  brain,  for 

instance,  can    use   the 


SMALL 

'INTESTINE 


FIG.  46.     The  digestive  organs. 


beefsteak  or  the  potato 
that  lies  on  your  plate, 
many  changes  must  be 
made  in  these  foods. 
We  therefore  have  a 
great  system  of  organs 
whose  business  it  is  to 
work  over  and  prepare 
the  foods  for  the  cells. 
These  are  the  digestive 
organs.  Of  all  parts 
of  the  body,  it  is  the 
most  important  to  un- 
derstand the  digestive 
system,  for  oftener 
than  any  other  part  of 
the  body,  these  organs 
fail  in  their  work,  and 
interfere  with  the 
health. 

The   Digestive    Sys- 


tem. 


The  digestive  system  includes  the  alimentary  canal  and 
88 


THE  DIGESTIVE  ORGANS 


89 


certain  accessory  or  assisting  organs  of  digestion,  —  the  teeth, 
salivary  glands  (Fig.  54),  liver,  and  pancreas.  The  alimen- 
tary canal  is  a  long  passageway  through  the  body,  into  which 
the  food  is  taken  while  it  is  being  digested.  The  teeth  grind 
the  food  into  small  pieces,  and  the  other  accessory  organs  of 
digestion  pour  juices  into  the  alimentary  canal  that  assist  in 
digesting  the  food.  Before  beginning  the  study  of  the  diges- 
tive organs  it  is  well  to  have  a  general  idea  of  the  structure 
and  function  of  a  gland,  for 
the  whole  digestive  system  is 
in  the  main  a  collection  of 
glands. 

A  Simple  Gland.  In  a  simple 
gland  the  cells  are  arranged 
in  the  form  of  a  hollow  tube 
(Fig.  47).  On  one  side  the 
gland  cells  take  in  water  and 
other  materials  from  the  blood. 
On  the  other  side  the  gland 
cells  give  off  a  liquid  into  the 
hollow  in  the  center  of  the 
gland.  When  the  gland  cells 
give  off  liquid1  the  liquid  Fia  47> 
flows  out  of  the  mouth 
of  the  gland.  The  gland  is  then  said  to  secrete,  and  the 
liquid  from  a  gland  is  called  the  secretion  of  the  gland. 


A  section  through  a  simple 
gland. 


1  In  some  glands  the  cells  merely  take  up  on  one  side  materials  from  the 
blood,  and  on  the  other  side  give  off  the  same  materials  into  the  central  opening 
of  the  gland.  A  sweat  gland  is  an  example  of  this  class  of  glands.  The  water 
and  the  salt  of  the  perspiration  merely  flow  from  the  blood  through  the  cells  of 
the  gland,  and  come  out  on  the  skin  as  sweat.  Other  glands  build  up  new  sub- 
stances with  the  materials  which  they  take  from  the  blood.  The  glands  of  the 


HUMAN  PHYSIOLOGY 


THE  ALIMENTARY   CANAL 

The  alimentary  canal  is  almost  thirty  feet  in  length.  Its 
principal  divisions  are  the  month,  pJiarynx  (throat),  esophagus, 
stomach,  and  the  small  and  large  intestine.  In  its  walls  are 
muscles  that  contract  on  the  food  and  force  it  onward  through 
the  canal.  Beginning  with  the  lips,  the  alimentary  canal 


FIG.  48.    The  stomach,  liver,  and  pancreas. 

i'j  lined  throughout  with  a  smooth  mucous  membrane.  This 
differs  from  skin  in  having  a  pink  color  and  in  being  kept 
moist  with  sticky  mucus  (Fig.  6),  which  causes  the  food  to 
move  easily  along  in  its  course  through  the  alimentary  canal. 
The  Stomach.  The  food  is  taken  into  the  mouth,  passes 
back  through  the  pharynx,  and  goes  down  the  esophagus. 

stomach  are  examples  of  this  kind  of  glands.  The  cells  in  these  glands  build  up 
and  give  forth  in  their  secretion  a  substance  called  pepsin^  which  digests  the 
proteid  foods. 


THE  DIGESTIVE  ORGANS  91 

At  the  bottom  of  the  esophagus  is  the  stomach.  This  holds 
about  three  pints,  and  when  full  is  about  a  foot  long  and  four 
inches  through  in  the  thickest  part.  When  empty,  however, 
the  stomach  draws  up  and  occupies  much  less  space.  The 
function  of  the  stomach  is  to  serve  as  a  storehouse  for  food  so 
that  enough  can  be  eaten  at  one  time  to  supply  the  body  for 
several  hours,  and  also  to  secrete  gastric  juice. 

The  Glands  of  the  Stomach.      In  the   inner  coat  of   the 
stomach  wall  are  great   numbers   of  gastric  glands,  which 


INNER  SURFACE  OF  STOMACH 


OUTER  CONNECTIVE 
TISSUE    COAT 


OBLIQUE    MUSCLES  CIRCULAR    MUSCLES        LONGITUDINAL    MUSCLES 


FlG.  49.     A  section  of  the  wall  of  the  stomach,  showing  muscles  and  glands.    B  is 
one  of  the  glands  more  highly  magnified. 

secrete  gastric  juice  for  digesting  the  food  and  for  killing 
bacteria.  Each  gland  is  a  little  circular  depression  (like 
a  little  well)  in  the  wall  of  the  stomach.  If  a  handkerchief 
be  spread  over  the  hand  and  thrust  down  into  the  hand 


HUMAN  PHYSIOLOGY 


FIG.  50.  To  illustrate  how 
a  gastric  gland  is  formed  by 
an  infolding  of  the  stomach 
wall. 


with  a  pencil  as  you  see  in  Figure  50,  the  shape  of  a  simple 
gastric  gland,  and  the  way  it  lies  in  the  stomach  wall,  will  be 
very  well  represented.  Some  of  the 
gastric  glands  branch  in  their  lower 
parts ;  but  they  are  all  formed  by 
folding  the  inner  layer  of  the  stomach 
wall  into  deep  narrow  pockets. 
Figure  49  shows  how  closely  these 
glands  are  packed  together,  and  it 
also  shows  how  small  they  must  be, 
for  they  do  not  reach  more  than 
halfway  through  the  stomach  wall, 
although  the  wall  itself  is  little 
thicker  than  a  piece  of  heavy  cloth. 
The  Gastric  Juice.  From  two  and  a 
half  to  five  quarts  of  gastric  juice  are  secreted  in  a  day. 
Most  of  the  gastric  juice  is  water,  but  it  contains  pepsin  for 
digesting  the  proteid  food,  and  acid.  The  acid  kills  many 
bacteria,  thus  keeping  them  from  getting  into  the  intestine 
and  causing  trouble  there.  It  is  useful  in  digestion  also,  since 
without  the  acid  the  pepsin  is  unable  to  digest  the  proteid 
foods. 

The  Muscles  of  the  Stomach.  The  entire  alimentary  canal 
from  the  top  of  the  esophagus  onward,  has  a  circular  and  a 
longitudinal  layer  of  muscles  in  its  walls.  The  stomach  has 
these  two  muscle  layers,  and  has  in  addition  a  layer  of  oblique 
muscles.  There  are,  therefore,  circular  muscles  running 
around  the  stomach,  longitudinal  muscles  running  lengthwise 
of  the  stomach,  and  oblique  muscles  running  slantingly  in  the 
stomach  walls.  These  muscles  force  the  food  onward  through 
the  stomach ;  and  during  digestion,  especially  in  the  lower  part 
of  the  stomach,  the  muscles  keep  contracting  and  mixing  up 


THE  DIGESTIVE  ORGANS 


93 


the  food  in  the  gastric  juice.  At  the  pylorus,  or  point  where 
the  stomach  joins  the  small  intestine,  the  circular  muscles  are 
thickened  into  a  strong  ring,  the  pyloric  muscle,  which  closes 
the  opening  between  the  stomach  and  intestine  while  diges- 
tion is  going  on  in  the  stomach.  After  stomach  digestion 
has  been  finished,  the  circular  muscles  contract  above  the 
food,  the  pyloric  muscle  opens  at  the  same  time,  and  the  food 
is  forced  into  the  intestine  (page  112). 

The  Small  Intestine.  The  small  intestine  is  coiled  in  the 
abdominal  cavity.  It  is  much  the  longest  part  of  the  alimen- 
tary canal,  having  a  length 
of  nearly  twenty-two  feet. 
In  its  walls  a"re  intestinal 
glands,  very  similar  to  the 
glands  of  the  stomach. 
They  secrete  the  intestinal 
juice,  which  aids  in  digest- 
ing the  food.  The  juices 
of  the  liver  and  of  the 
pancreas  are  also  emptied 
into  the  small  intestine,  and 
the  digestion  carried  on 
here  is  even  more  impor- 
tant than  the  digestion  in 

the    Stomach.1 


Villi  and  intestinal  glands. 


The  Villi.  On  the  intestinal  wall  are  many  little  finger- 
like  projections  called  villi  (singular,  villus),  which  stand  up 
in  the  digested  food  and  absorb  it,  or  take  it  into  the  body 
through  the  intestinal  wall.  So  abundant  are  the  villi  that 

1  In  a  few  cases  the  stomach  has  been  removed  and  the  esophagus  connected  with  the 
small  intestine.  Persons  on  whom  this  operation  has  been  performed  have  lived,  the 
digestive  work  of  the  stomach  being  done  by  the  small  intestine. 


94  HUMAN  PHYSIOLOGY 

they  give  the  inner  surface  of  the  intestinal  wall  an  appear- 
ance like  velvet,  and  they  absorb  the  food  much  more 
rapidly1  than  a  smooth,  even  wall  could  do.  Digestion  is 
finished  in  the  small  intestine,  and  most  of  the  liquids  and 
the  digested  food  are  absorbed  before  the  large  intestine  is 
reached.  A  little  food,  however,  passes  into  the  large  intes- 
tine and  is  there  absorbed  while  the  muscles  in  the  walls  of 
the  large  intestine  move  onward  the  indigestible  material. 

The  Large  Intestine.  The  large  intestine  begins  low 
down  in  the  right  side  of  the  abdominal  cavity,  passes  up  the 
right  side,  then  across  under  the  diaphragm,  and  down  the  left 
side.  Just  below  where  the  small  intestine  opens  into  it  there 
is  a  small,  worm-like  structure  (Fig.  46),  the  'vermiform 
appendix?  The  large  intestine  has  no  villi.  Its  glands 
secrete  mucus  and  also  throw  off  into  the  intestine  some 
waste  products  from  the  body. 

THE  ACCESSORY  ORGANS  OF  DIGESTION 

The  Teeth.  A  tooth  is  composed  of  a  crown,  a  neck,  and 
one  or  more  roots.  The  roots  stand  in  sockets  in  the  jaw- 
bones, and  are  held  in  place  by  a  hard,  bone-like  cement. 
The  outer  coat  of  the  crown  is  made  of  enamel,  the  hardest 
material  in  the  body.  Under  the  enamel  and  forming  the 
main  bulk  of  the  tooth  is  the  dentine?  a  substance  harder 
than  the  most  compact  bone,  but  not  nearly  so  hard  as 

1  The  villi  give  from  four  to  eight  times  as  much  absorbing  surface  as  the 
smooth  walls  of  the  intestine  would  give. 

2  The  disease  called  appendicitis  is  caused  by  germs  growing  in  the  vermiform 
appendix  and  causing  inflammation.      In  severe  cases  of  appendicitis,  it  may  be 
necessary  to  open  the  abdominal  cavity  and  remove  the  vermiform  appendix. 

3  Ivory  is  dentine,  usually  obtained  from  the  tusks  of  elephants,  but  sometimes 
from  the  tusks  of  the  walrus  or  the  teeth  of  the  hippopotamus. 


THE  DIGESTIVE  ORGANS 


95 


enamel.  In  the  middle  of  the  tooth  is  the  pulp  cavity,  a  little 
chamber  containing  nerves  and  blood  vessels.  Get  a  tooth 
from  a  dentist,  or  find  the  tooth  of  an  animal,  and  break  it 
open,  and  you  will  have  no  difficulty  in  finding  the  enamel, 
the  dentine,  the  pulp  cavity,  and 
the  little  root  canals  through 
which  the  nerves  and  blood 
vessels  come  up  from  the  jaw- 
bone into  the  tooth. 

Different  Kinds  of  Teeth  and 
their  Functions.  There  are  four 
kinds  of  teeth,  —  incisors,  canines 
or  cuspids,  bicuspids,  and  molars. 
The  incisors  are  flat  and  sharp 
for  biting  off  food.  In  the  dog 
and  other  flesh-eating  animals 
the  canines  are  tusks  which  are 
used  as  weapons  and  in  tearing 

flesh,  but  in  man  their  principal  use  is  to  assist  the  incisors  in 
biting.  The  bicuspids  and  the  molars  have  wide  surfaces  for 
grinding  the  food  into  small  pieces  and  mixing  it  thoroughly 
with  the  saliva.  Examine  a  back  tooth  and  notice  the  cusps, 
or  points,  on  it.  Observe  how  the  cusps  of  the  upper  and 
lower  teeth  fit  into  each  other  when  the  jaws  are  tightly 
closed.  Then  notice  how  the  jaws  move  sidewise  in  chewing, 
and  you  will  readily  understand  how  the  food  is  crushed  and 
ground  to  pieces  as  the  teeth  slide  across  each  other. 

Temporary  and  Permanent  Teeth.  The  jaws  in  childhood 
are  too  small  to  hold  the  large  teeth  which  we  need  in  later  life. 
In  early  life  we  have  therefore  a  set  of  twenty  small  tempo- 
rary teeth,  and  in  later  life  a  set  of  thirty- two  larger  permanent 
teeth.  The  earliest  permanent  teeth  to  appear  are  the  first 


FIG.  52.     Section  of  a  tooth. 


96  HUMAN  PHYSIOLOGY 

molars,1  which  come  in  behind  the  temporary  molars  about 
the  sixth  or  seventh  year. 

Care  of  the  Teeth.  Decay  of  the  teeth  is  caused  by  bacteria, 
which  find  a  splendid  place  to  grow  in  the  moist,  warm  food 
between  the  teeth.  It  is  also  thought  that  bacteria  are  the 


FIG.  53.     One  half  of  the  permanent  teeth. 

cause  of  tartar,  a  dark  hard  substance  that  collects  on  the 
teeth  of  some  persons.  It  is  evident  that  the  best  way  to 
preserve  the  teeth  and  to  keep  them  white  and  beautiful  is 
to  keep  them  clean,  so  that  bacteria  will  find  no  food 
materials  among  them.  They  should  be  brushed  with  pure 
soap  or  a  good  tooth  powder  after  each  meal,  or  at  least  in 
the  morning  and  at  night  before  going  to  bed.  Particles  of 
food  should  be  removed  from  between  the  teeth  with  a  wooden 
or  quill  toothpick,  or  with  a  piece  of  thread.  It  is  very 

1  A  common  error  is  to  mistake  the  first  permanent  molars  for  temporary  teeth, 
and  to  allow  them  to  decay,  thinking  that  they  will  be  replaced  by  new  teeth. 
When  there  are  three  double  teeth  on  one  side  of  the  jaw,  the  back  one  is  a 
permanent  tooth. 


THE  DIGESTIVE  ORGANS 


97 


important  not  to  break  the  enamel  by  biting  on  thread,  nuts, 
or  other  hard  substances;  for  where  the  enamel  is  broken  and 
the  dentine  exposed,  decay  soon  follows.  Tartar  should  be 
removed  by  a  dentist,  for  it  causes  the  gums  to  shrink  and 
expose  the  necks  of  the  teeth  below  the  enamel. 

When  decay  has  begun  in  a  tooth,  the  only  remedy  is  to 
have  the  cavity  filled  by  a  dentist.  This  should  be  done 
before  the  cavity  becomes  large  and  gets  down  close  to  the 
nerves  in  the  pulp  cavity  of  the  tooth.  The  teeth  are  so 
valuable  that  we  cannot  afford  to  lose  them,  and  it  is  far 
better  to  have  a  dentist  look  them  over  occasionally  and  fill 
all  small  cavities  than  it  is  to  suffer  later  from  toothache, 
neuralgia,  and  indigestion,  and  to  pay  for  crowns,  bridge 
work,  or  artificial  teeth. 

The  Salivary  Glands.  There  are  six  salivary  glands, — three 
pairs.  The  two  stiblingual  glands  are  under  the  tongue,  the 
submaxillary  glands  are  under 
and  behind  the  corners  of  the 
lower  jaws,  and  the  parotid^- 
glands  are  in  front  of  the  ears. 
The  saliva  is  carried  from  the 
glands  to  the  mouth  through 
circular  canals  called  ducts. 
The  ducts  of  the  submaxillary 
and  of  the  sublingual  glands  of 
each  side  of  the  head  unite  DUCT 
before  they  enter  the  mouth. 
The  ducts  from  the  parotid 
gland  open  on  the  inside  of 


PAROTID  GLAND 


SUBMAXILLARY 
GLAND 


SUBLINGUAL  GLAND 


FlG.  54.     The  salivary  glands. 


the  cheeks  opposite  the  second  molars  of  the  upper  jaw.     The 

1  In  mumps  the  parotid  glands  are  swollen  and  inflamed.     The  other  salivary 
glands  also  are  occasionally  affected. 


98 


HUMAN  PHYSIOLOGY 


saliva  is  secreted  by  the  cells  in  the 
small  branches  of  the  gland  (Fig.  55) 
and  flows  into  the  main  duct  and  on 
into  the  mouth. 

Uses  of  the  Saliva.  The  saliva 
moistens  food  and  makes  it  possible 
to  swallow  dry  food  like  crackers, 
which  without  saliva  would  become 
dust  in  the  mouth.  The  saliva  is 
useful  also  because  it  contains  a 
substance  called  ptyalin,  which  di- 
gests starch. 

The  Pancreas.  The  pancreas  (Fig. 
48)  is  a  long  gland,  shaped  something 
like  the  tongue  of  a  dog.  The  Ger- 
mans call  the  pancreas  the  "  abdomi- 
nal salivary  gland,"  and  this  is  a  very 
good  name  for  it,  for  it  is  composed 
of  many  little  branches,  like  a  great 
salivary  gland,  and  the  pancreatic 
juice  is  very  much  like  thin,  watery 
FIG.  55.  Diagram  of  a  longitu-  saliva.  The  pancreas  is  the  most 

dinal  section  of  a  salivary  gland.     .  r     , ,    .        1 .  .  ,        , 

A  salivary  gland  is  formed  by  important  of  all  the  digestive  glands, 
folding  in  the  lining  of  the  mouth  for   the    pancreatic    juice    contains 

in  the  same  way  that  a  gastric    trypsin     a     substance    which    digests 
gland  is  formed  by  folding  in  the       *f        ' 

lining  of  the  stomach.   The  dif-   proteids,    amylopsin     for     digesting 
ference  in  the  plan  of  the  two   starches,  and  steapsin  for  digesting 

glands   is   that    a    gastric    gland     r  ,-,-,,  ..       .     .  -,. 

branches  only  a  few  times,  while    fats«       The    Pancreatic   JU1C6    digests 
a  salivary  gland  has  hundreds  of    all     three     classes      of      foods     Very 

branches-  rapidly,    and    it    is    principally   the 

action    of   this  juice  that   makes  the  digestion  in  the  small 
intestine  so  important. 


THE  DIGESTIVE  ORGANS  99 

The  Liver.  The  liver  is  the  largest  gland  in  the  body; 
it  weighs  from  three  and  a  half  to  four  pounds.  It  lies  in 
the  right  side  of  the  abdominal  cavity  close  up  to  the  dia- 
phragm, one  lobe  running  down  close  to  the  body  wall  and 
another  extending  across  under  the  diaphragm  and  covering 
the  inner  end  of  the  stomach.  The  liver  cells  secrete  bile, 
and  running  all  through  the  liver  is  a  system  of  little  ducts 
that  collect  the  bile  and  bring  it  all  to  one  large  bile  duct. 
This  large  duct  empties  into  the  upper  part  of  the  small 
intestine. 

On  the  under  side  of  the  liver  is  a  little  pear-shaped  sac, 
called  the  gall  bladder  (Fig.  48).  When  digestion  is  not 
going  on,  the  opening  of  the  bile  duct  into  the  small  intestine 
closes,  and  the  bile  passes  into  the  gall  bladder,  where  it  is 
stored.  Then  when  food  passes  into  the  small  intestine  for 
digestion,  the  mouth  of  the  bile  duct  opens  and  the  walls  of 
the  gall  bladder  contract,  sending  into  the  intestine  a  flood 
of  greenish-yellow  bile.  In  a  later  chapter  we  shall  study 
about  other  important  functions  of  the  liver. 

The  Digestive  System  as  a  Whole.  The  alimentary  canal 
may  be  compared  to  a  long  channel  through  the  body,  and 
the  cells  of  the  digestive  organs  to  workers  who  are  stationed 
along  the  sides  of  the  canal  to  prepare  the  foods  for  use  by 
pouring  digestive  juices  over  them  as  they  pass  along  the 
canal. 

In  the  mouth  the  food  is  ground  into  fine  pieces  and  mixed 
with  saliva,  and  the  ptyalin  in  the  saliva  immediately  starts 
the  process  of  digestion.  Then  the  journey  through  the  long 
canal  begins  in  earnest,  the  cells  of  the  stomach,  intestine, 
pancreas,  and  liver  pouring  in  their  juices  as  the  food  reaches 
their  parts  of  the  canal.  On  and  on  the  food  is  moved,  the 
juices  digesting  it  and  the  digested  portion  being  absorbed, 


100  HUMAN  PHYSIOLOGY 

until  finally  only  the  indigestible  matter  of  the  food  stuffs 
remains. 

The  digestive  juices  can  work  outside  of  the  body  as  well 
as  in  the  alimentary  canal,  and  it  might  be  possible  to  arrange 
a  digestive  system  according  to  a  plan  differing  from  that 
which  nature  has  used  in  our  bodies.  Yet  you  would  have 
difficulty  in  thinking  of  anything  simpler  or  better  for  diges- 
tion and  absorption  than  a  long  tube  through  the  body,  into 
which  the  foods  can  be  taken  and  soaked  in  digestive  juices 
while  they  are  slowly  moved  along. 

The  Nervous  Control  of  the  Digestive  System.  The  diges- 
tive organs,  like  other  parts  of  the  body,  are  controlled  by 
the  nervous  system.  Most  of  the  work  of  regulating  these 
organs  is  done  through  the  sympathetic  nervous  system,  and 
it  is  carried  on  without  our  knowledge  and  without  any  atten- 
tion from  the  mind.  The  salivary  glands  and  the  glands  of 
the  stomach,  however,  are  controlled  to  a  certain  extent  by 
the  higher  centers  of  the  brain,  and  the  mind  has  a  very  great 
effect  on  them.  You  perhaps  know  how,  when  you  are  hun- 
gry, the  sight  or  odor  of  food  will  "  make  the  mouth  water." 
This  means  that  at  the  mere  thought  of  food  the  nervous 
system  starts  the  salivary  glands  to  work.  The  gastric 
glands  also  are  influenced  by  the  mind,  as  the  following 
experiments  on  a  dog  showed : 

The  esophagus  of  a  dog  was  divided,  and  when  the  animal 
was  hungry,  he  was  given  some  fresh  beef.  The  dog  thought 
he  was  eating  a  good  dinner,  but  a  tube  had  been  connected 
to  the  esophagus  in  such  a  way  that  the  beef  did  not  go  into 
the  stomach  but  into  a  dish  beside  the  dog.  Nevertheless, 
the  gastric  glands  promptly  began  to  pour  gastric  juices 
into  the  stomach.  Merely  showing  the  food  to  the  dog  was 
enough  to  start  the  secretion  of  the  glands.  The  experiment 


! 


THE  DIGESTIVE  ORGANS  ioi 


showed  clearly  that  the  mind  affects  the  glands  of  the  stomach 
as  well  as  the  salivary  glands. 

At  another  time  a  tube  was  fitted  to  the  part  of  the  esopha- 
gus which  was  connected  with  the  stomach,  and  beef  was 
introduced  into  the  stomach  without  the  dog's  knowing  that 
he  was  being  fed.  In  this  case,  the  ^gastric  juice  was 
secreted  very  slowly,  and  the  meat  lay  in  t^e>  ^tomach  a  long 
time  before  it  was  digested.  ,'"v  >  ,  >,,,,,  •,/<; 

These  experiments  show  plainly  that'  the"  rJerv'dus^sy&tdro; 
has  a  great  effect  on  the  digestive  organs,  since  the  taste  or 
smell  of  food,  or  even  the  sight  of  food,  will  start  the 
secretions  to  flowing  from  some  of  the  digestive  glands. 
They  teach  us  that  it  is  very  important  for  our  food  to  be 
pleat  ant  to  the  taste,  in  order  that  a  good  supply  of  juices 
may  be  secreted  to  digest  it.  They  show  how  indigestion 
may  b^  caused  by  eating  food  which  is  distasteful,  and  by 
eating  when  food  is  not  wanted.  They  also  explain  some 
things  which  have  long  been  known,  —  that  a  cheerful,  happy 
life  brings  with  it  a  good  digestion ;  and  that  anger,  quarrel- 
ing, melancholy,  sorrow,  homesickness,  and  pain  interfere 
with  the  digestion  of  the  food.  Our  food  should  therefore 
be  well  cooked  and  served  in  an  appetizing  manner ;  every 
one  should  come  to  the  table  in  a  cheerful  frame  of  mind, 
and  should  avoid  all  disagreeable  topics  of  conversation,  and 
all  unpleasant  thoughts  should  be  laid  aside  until  the  meal  is 
over.  "  Laugh  and  grow  fat "  is  a  wise  old  saying  which  we 
would  do  well  to  heed. 

Alcohol  and  the  Digestive  Organs.  Strong  alcohol  is  ex- 
ceedingly injurious  to  living  cells.  The  stomach  and  the 
liver  get  in  its  strongest  form  the  alcohol  which  is  taken  into 
the  alimentary  canal,  and  these  are  the  digestive  organs  most 
injured  by  alcohol.  Strong  alcoholic  drinks  taken  into  the 


102  HUMAN"  PHYSIOLOGY 

stomach  cause  inflammation  of  the  lining  of  the  stomach.  If 
taken  often,  they  may  cause  catarrh  of  the  stomach.  They 
are  especially  harmful  if  taken  when  the  stomach  is  empty. 
Alcohol  taken  at  mealtime  is  diluted  by  the  food  and  liquids 
in  the  stomach,  and  its  effect  on  the  mucous  membrane  of 
the  stomach  is  therefore  weakened.  Practically  all  alcohol 
taken  into  the*  -alimentary  canal  is  absorbed  through  the  stom- 
ach walls,  and.  therefore  the  intestine  is  little  affected  by  it. 
•  ' After  the  alcohol  is  absorbed  from  the  stomach  it  is  car- 
ried to  the  liver.  The  two  chief  diseases  of  the  liver,  due  to 
alcohol,  are  fatty  degeneration,  caused  by  beer,  ale,  and  other 
malt  liquors,  and  hardening  of  the  liver,  caused  by  whisky, 
gin,  rum,  brandy,  and  other  distilled  liquors.  In  fatty  degen- 
eration, the  living  protoplasm  of  the  liver  cell  is  replaced  by 
fat,  and  finally  each  cell  becomes  a  little  sac  of  fat,  unable 
to  manufacture  bile  or  to  do  the  other  work  of  a  liver  cell. 
In  hardening  of  the  liver,  the  connective  tissue  of  the  organ 
grows  far  too  abundantly,  and  by  contracting  squeezes  the 
delicate  blood  vessels  and  liver  cells.  This  greatly  hinders 
the  work  of  the  liver,  and  may  even  cause  the  liver  cells  to 
waste  away  and  die.  Either  one  of  these  diseases  may  cause 
death,  hardening  of  the  liver  being  a  common  cause  of  death 
among  excessive  drinkers. 


THE  DIGESTIVE  ORGANS  OF  OTHER  ANIMALS 

A  starfish  throws  its  stomach  out  of  its  mouth  and  wraps 
it  about  the  oyster  or  other  animal  that  it  wishes  to  eat. 
A  snake  has  jaws  fastened  together  with  ligaments  so  elastic 
that  it  swallows  whole  animals  thicker  than  its  own  body. 
An  elephant  feeds  itself  with  its  trunk,  which  corresponds 
to  the  nose  in  other  animals.  There  are  many  other  things 


THE  DIGESTIVE  ORGANS  103 


connected  with  the  digestive  systems  and  food  habits  of  ani- 
mals that  are  very  different  from  anything  that  is  found  in 
man. 

Teeth.  Beetles,  grasshoppers,  and  crustaceans 1  have  no 
teeth,  but  have  horny  jaws  which  work  sideways  instead  of  up 
and  down  as  our  jaws  work.  Some  fish  have  teeth,  but  many 
have  none.  A  frog  has  teeth  in  its  upper  jaw,  and  a  toad 
has  no  teeth  in  either  jaw.  All  the  reptiles  have  teeth  ex- 
cept the  turtle  tribe,  which,  like  the  birds,  have  horny,  tooth- 
less beaks.  In  the  poisonous  snakes,  two  of  the  salivary 
glands  secrete  poison,  or  venom,  instead  of  saliva,  and  two  of 
the  teeth  are  long,  hollow  fangs  through  which  the  venom  is 
injected  into  whatever  the  snake  strikes. 

The  teeth  of  mammals  differ  very  much  according  to  the 
food  which  they  eat.  Rodents  have  long,  chisel-like  incisors 
for  gnawing.  The  carnivora  have  long  canines  for  killing 
their  prey  and  tearing  the  flesh  on  which  they  feed.  The 
herbivora  have  broad  back  teeth  for  grinding  the  grass  and 
leaves  which  they  eat. 

Among  the  herbivorous  animals  are  many  interesting 
differences  in  the  number  and  arrangement  of  the  teeth.  An 
elephant  has  ten  teeth,  —  two  upper  incisors  (the  tusks)  and 
eight  molars.  A  cow  has  six  incisors  and  two  canines  in  the 
lower  jaw,  and  no  incisors  or  canines  in  the  upper  jaw.  A 
horse  has  six  incisors  and  two  canines  in  each  jaw,  but  the 
canines  do  not  come  through  until  about  the  sixth  year.  You 
can  therefore  tell  something  about  the  age  of  a  horse  by 
looking  at  his  teeth.  If  he  has  eight  front  teeth  in  each  jaw, 
he  is  over  six  years  old.  In  both  the  cow  and  the  horse  there 
is  a  wide  space  between  the  canines  and  the  back  teeth. 

1  Hard-shelled  animals  with  jointed  legs,  like  the  crab,  crayfish,  lobster,  etc. 


104 


HUMAN  PHYSIOLOGY 


Tongues.  A  frog's  tongue  is  fastened  near  the  front  of  the 
mouth,  and  lies  with  its  tip. pointing  backward  in  the  mouth. 
So  quickly  that  the  eye  cannot  follow  it,  the  frog  can  throw 


FIG.  56.    A  frog's  tongue. 


its  tongue  over  forward  and  out  of  its  mouth  to  catch  an 
insect.  The  lizard  also  catches  insects  by  shooting  out  the 
tongue.  In  this  way  some  small  lizards  pick  up  from  one 
thousand  to  fifteen  hundred  ants  at  one  feeding.  A  snake 
uses  its  forked  tongue  for  feeling,  and  possibly  for  frighten- 
ing away  those  who  might  attack  it ;  but  a  snake  does  no 


FIG.  57.     A  chameleon  catching  a  moth.    The  chameleons  are  closely  related  to  the 
lizards.    The  tongue  can  be  extended  six  or  eight  inches  with  lightning-like  rapidity. 

harm  with  its  tongue.  The  tongues  of  carnivorous  mammals 
are  covered  with  sharp  little  points  for  cleaning  the  last 
particles  of  meat  from  bones.  The  giraffe  can  stretch  out 
its  tongue  until  it  is  eighteen  inches  long,  to  gather  in  the 
leaves  on  which  it  feeds. 


THE  DIGESTIVE  ORGANS 


105 


Other  Digestive  Organs.  Crustaceans  have  a  gastric  mill 
in  the  stomach.  On  the  inside  of  the  stomach  wall  there  are 
bony  plates  which  are  rubbed  together  to  grind  up  the  food. 
A  chicken  (like  other  birds)  softens  its  food  in  a  crop,  or  wide 
place  in  the  esophagus,  and  then,  with  small  stones  which  it 
swallows,  grinds  the  food  in  the  gizzard,  or  thick-walled  back 
part  of  the  stomach. 

The  ruminants,  or  cud-chewing  animals  (cattle,  sheep, 
goats,  deer,  antelope,  camels,  and  giraffes),  have  the  stomach 


FIG.  58.    The  stomach  of  a  ruminant. 

in  four  parts  or  divisions.  They  have  also  two  openings  from 
the  esophagus  into  the  stomach,  one  a  longitudinal  slit  in  the 
side  of  the  wall  opening  into  the  first  division  of  the  stomach, 
and  the  other  the  usual  opening  at  the  bottom  of  the 
esophagus  leading  into  the  second  stomach.  The  food  is 
first  swallowed  without  much  chewing,  and  the  ball  of  grass 
or  other  coarse  material  stretches  the  esophagus  wall,  opens 
the  slit  in  its  side,  and  drops  into  the  first  division  of  the 
stomach.  It  is  either  stored  here  or  passed  on  into  the  sec- 
ond division  and  stored  there.  Then,  when  the  animal  has 
finished  eating,  the  food  is  brought  up,  a  mouthful  at  a  time, 


106  HUMAN  PHYSIOLOGY 

and  rechewed.  When  it  is  swallowed  the  second  time  it  is 
so  soft  and  pasty  that  it  fails  to  open  the  slit  in  the  esophagus 
wall,  but  passes  through  the  upper  part  of  the  second  division 
of  the  stomach  into  the  third  stomach.  From  there  it  is 
quickly  passed  into  the  fourth  or  true  stomach,  where  it  is 
digested. 

In  their  wild  state  the  cud-chewing  animals  are  eaten  by 
the  carnivora,  and  this  kind  of  stomach  is  an  advantage  to 
them,  since  they  can  gather  their  food  quickly  and  swallow 
it,  and  then  hide  in  a  safe  place  while  they  chew  it  at  their 
leisure. 

In  addition  to  the  four  divisions  found  in  the  stomachs  of 
other  ruminants,  the  camel  has  little  sacs,  formed  by  folding  the 
stomach  wall  into  pouches  or  pockets,  in  which  water  is  stored. 
A  muscle  runs  around  the  mouth  of  each  sac  and  closes  it 
tightly,  holding  the  water  in  until  it  is  needed.  At  the  right 
time  the  muscle  closing  the  sac  relaxes,  letting  the  water  flow 
into  the  stomach. 

The  intestine  of  the  carnivorous  animals  is  short,  and  that 
of  the  herbivorous  animals  long,  the  ox  having  an  intestine 
about  one  hundred  and  fifty  feet  in  length.  Judging  from  the 
human  teeth  and  other  digestive  organs,  man  seems  to  be  mid- 
way between  the  herbivorous  and  carnivorous  animals.  We 
may  therefore  conclude  that  nature  intends  that  man  should 
eat  both  vegetable  and  animal  food. 

Summary.  Before  the  foods  can  be  used  by  the  cells  they 
must  be  digested.  This  work  is  done  by  the  organs  of  the 
digestive  system,  which  is  composed  of  the  alimentary  canal 
and  the  accessory  organs  of  digestion.  In  the  main  the 
digestive  organs  are  glands  that  take  material  from  the  blood 
and  manufacture  digestive  juices. 

The  alimentary  canal  is  nearly  thirty  feet  in  length.     It 


THE  DIGESTIVE  ORGAN'S  IO/ 

has  muscles  in  its  walls  that  move  the  food  onward,  and  is 
lined  with  mucous  membrane.  The  stomach  holds  about 
three  pints.  It  serves  as  a  storehouse  for  food,  and  the 
glands  in  its  wall  secrete  the  gastric  juice.  The  gastric  juice 
contains  pepsin  for  digesting  proteid  foods,  and  acid  which 
assists  in  digestion  and  kills  bacteria.  The  small  intestine 
is  about  twenty-two  feet  in  length.  Its  glands  secrete  the 
intestinal  juice,  and  the  villi  on  its  walls  absorb  the  digested 
food.  The  glands  of  the  large  intestine  secrete  mucus  and 
throw  off  wastes  from  the  body. 

The  body  of  a  tooth  is  composed  of  dentine.  Its  crown  is 
covered  with  hard  enamel  and  it  has  a  pulp  cavity  in  its 
center.  The  four  kinds  of  teeth  are  incisors,  canines,  bicus- 
pids, and  molars.  There  are  twenty  teeth  in  the  temporary 
set  and  thirty  in  the  permanent  set.  Decay  of  the  teeth  is 
caused  by  bacteria  that  grow  in  the  food  material  that  clings  to 
the  teeth.  The  way  to  prevent  decay  is  to  keep  the  teeth  clean. 

There  are  three  pairs  of  salivary  glands,  —  the  sublingual, 
submaxillary,  and  parotid.  They  secrete  saliva  which 
moistens  the  food  and  contains  ptyalin  for  digesting  starch. 
The  pancreas  pours  pancreatic  juice  into  the  small  intestine. 
This  juice  contains  trypsin  for  digesting  proteid,  amylopsin 
for  digesting  starch,  and  steapsin  for  digesting  fat.  The 
liver  secretes  bile,  which  is  stored  in  the  gall  bladder  until 
needed  in  the  small  intestine. 

The  alimentary  canal  is  a  long  channel  through  the  body 
into  which  the  food  is  taken  and  moved  along,  while  diges- 
tive juices  are  poured  over  it.  As  the  food  moves  along  it  is 
digested  and  absorbed.  The  salivary  glands  and  the  stomach 
are  greatly  influenced  by  the  mind,  and  a  contented,  happy 
life  greatly  aids  in  keeping  the  digestive  organs  in  good  con- 
dition. 


108  HUMAN  PHYSIOLOGY 

Alcohol  causes  inflammation  of  the  stomach  and  fatty  degen- 
eration and  hardening  of  the  liver.  It  is  exceedingly  in- 
jurious to  the  digestive  organs  and  should  not  be  taken  into 
the  alimentary  canal. 

The  digestive  organs  of  some  other  animals  are  very  dif- 
ferent from  our  own. 

QUESTIONS 

\*Why  do  we  need  a  digestive  system  ?  'MVhat  does  the  digestive 
system  include  ?  Name  the  accessory  organs  of  digestion.  Describe 
the  alimentary  canal,  v^ What  is  the  function  of  the  teeth?  of  the 
other  accessory  organs  of  digestion?  Of  what  in  the  main  is  the 
digestive  system  composed? 

How  are  the  cells  arranged  in  a  simple  gland?  What  do  these 
cells  do  ?  What  is  meant  by  the  word  secrete  ?  secretion  ? 

How  long  is  the  alimentary  canal?  Name  its  chief  divisions, 
is  the  food  moved  through  it?  With  what  is  it  lined?  How 
does  this  differ  from  skin? 

Locate  the  stomach  (page  17).  Trace  the  course  of  the  food  into 
the  stomach.  How  much  will  the  stomach  hold?  Give  its  dimen- 
sions when  full.  What  two  functions  has  the  stomach  ? 

What  is  the  function  of  the  gastric  glands  ?  Show  how  a  gland  is 
formed  in  the  wall  of  the  stomach.  How  much  gastric  juice  is 
secreted  in  a  day  ?  What  does  it  contain  ?  What  is  the  use  of  the 
pepsin  ?  Give  two  uses  of  the  acid.  Describe  the  muscles  of  the 
stomach.  What  two  functions  have  these  muscles?  What  and 
where  is  the  pyloric  muscle  and  what  is  its  function? 

How  long  is  the  small  intestine?  What  do  its  glands  secrete? 
What  juices  are  emptied  into  it?  Describe  the  villi.  What  is  their 
function?  What  and  where  is  the  vermiform  appendix?  What  is 
the  function  of  the  glands  of  the  large  intestine? 

Name  the  parts  of  a  tooth.  What  is  the  enamel?,  dentine?  the 
pulp  cavity?  What  is  in  the  pulp  cavity?  Name  the  four  kinds  of 


THE  DIGESTIVE  ORGANS  109 

teeth.  Give  the  function  of  each  kind.  How  many  teeth  in  the 
temporary  set?  in  the  permanent  set?  What  causes  decay  of  the 
teeth?  How  can  decay  be  prevented?  After  decay  has  started, 
what  should  be  done  ? 

Name  the  salivary  glands.  What  is  their  function?  What  two 
uses  has  saliva?  Locate  the  pancreas  (page  17).  What  does  it 
secrete?  What  three  substances  are  in  the  pancreatic  juice?  What 
does  each  digest?  Locate  the  liver.  How  large  is  it?  What  does 
it  secrete  ?  Where  is  the  gall  bladder  and  what  is  its  function  ? 

To  what  may  the  digestive  system  as  a  whole  be  compared  ?  What 
happens  to  food  as  it  is  moved  through  the  alimentary  canal? 

What  proof  is  there  that  the  mind  affects  the  secretion  of  the 
salivary  glands  ?  In  the  case  of  the  dog,  what  effect  on  the  gastric 
glands  had  the  idea  that  he  was  eating  ?  What  happened  when  the  dog 
was  fed  without  knowing  it?  What  do  these  experiments  show? 
Name  some  of  the  conditions  of  the  mind  that  may  interfere  with 
digestion. 

What  effect  has  alcohol  on  the  stomach?  on  the  liver? 

How  does  a  starfish  get  its  food  into  its  stomach?  What  is  peculiar 
about  the  way  a  snake  eats  ?  about  the  way  an  elephant  eats  ?  Tell 
something  about  the  teeth  of  different  animals. 

What  is  peculiar  about  the  tongue  of  a  frog?  Tell  something 
about  the  tongues  of  other  animals. 

What  is  peculiar  about  the  treatment  of  the  food  in  the  stomach 
of  a  crustacean  ?  of  a  bird  ?  Describe  the  stomach  of  a  ruminant  and 
the  course  of  the  food  through  it.  Of  what  advantage  is  this  kind 
of  stomach  to  a  ruminant  ?  Describe  the  stomach  of  a  camel. 


If  the  small  intestine  had  a  smooth  wall,  how  long  would  it  need 
to  be  to  have  the  same  absorbing  surface  that  it  now  has  (see  footnote, 
page  94)  ?  Explain  how  folding  the  wall  of  the  alimentary  canal  into 
deep  glands  greatly  increases  the  secreting  surface, 


CHAPTER   IX 


DIGESTION,   ABSORPTION,   AND  OXIDATION  OF  FOODS1 

Why  Food  must  be  digested.  When  food  has  been  taken 
into  the  alimentary  canal,  it  has  not  yet  really  entered  the 
body,  but  is  only  in  a  passageway  which  leads  through  the 
body.  To  get  into  the  body,  it  must  first  pass  through 
the  lining  of  the  alimentary  canal  into  the  blood.  Many  of 
our  foods  must  have  changes  made  in  them  before  they  can 
do  this,  and  the  following  experiments  will  show  one  of  the 
changes  which  is  necessary  in  many  foods: 

Drop  a  few  grains  of  salt  into  a 
glass  of  water  and  stir  it  up.  Does 
the  salt  dissolve  ?  Taste  the  water. 
Are  there  salt  molecules  in  all  parts 
of  the  water? 

Stir  some  clean  sand  into  another 
glass  of  water.  Does  the  sand  dis- 
solve? Do  its  molecules  separate 
and  go  out  through  the  water  as 
do  the  salt  molecules,  or  do  they 
remain  together? 

Fold  a   piece  of  soft   paper   in 
the  manner  indicated  in  Figure  59. 
Open  it  at  the  free  corners  and  set 
Pour  the  salt  water  into  the  paper.    Does 


FIG.  59. 
it  in  the  mouth  of  a  glass. 


xTo  THE  TEACHER:    The  whole  subject  of  the  nutrition  of  the  human  body  is 
far  from  elementary,  and  it  takes  careful  teaching  to  give  beginning  classes  any 
comprehension  of  it.     It  is  the  central  idea  in  physiology,  however,  and  under- 
HO 


DIGESTION'.   ABSORPTION,   AND   OXIDATION        in 

the  water  pass  through  the  paper  ?  Does  the  salt  pass  through  the 
paper?  Arrange  another  piece  of  paper  the  same  way  and  pour  into 
it  the  water  containing  sand.  Does  the  sand  pass  through  the  paper  ? 

When  a  substance  dissolves  in  a  liquid,  its  molecules 
separate.  When  it  does  not  dissolve,  they  remain  clinging 
together  in  a  great  mass.  The  single  molecules  of  salt  in 
the  water  readily  pass  through  the  paper ;  but  the  grains  of 
sand,  with  their  molecules  all  in  great  clusters,  are  caught  by 
the  paper  and  are  not  allowed  to  pass  through. 

Most  of  our  solid  foods  are  substances  that  do  not  dissolve 
in  water  or  in  the  juices  of  the  alimentary  canal.  Meat, 
butter,  eggs,  or  bread  would  lie  indefinitely  in  the  alimentary 
canal  without  dissolving  if  their  molecules  were  not  changed. 
They  must,  therefore,  be  digested,  or  changed  to  substances 
that  will  dissolve  in  the  stomach  and  intestine.  Digestion 
is  the  process  of  changing  foods  into  substances  that  will  dis- 
solve and  pass  through  the  walls  of  the  alimentary  canal  into 
the  blood. 

You  will  see  at  once  the  tremendous  importance  of  diges- 
tion, for  if  it  is  not  properly  performed,  the  food  which  should 
nourish  the  body  may  simply  pass  through  the  alimentary 
canal  and  never  get  to  the  cells  which  it  should  feed. 

Changes  in  the  Food  during  Digestion.  The  molecules  of 
food  are  large,  as  molecules  go,  a  starch  molecule  having  in  it 
four  hundred  and  fifty  atoms,  while  some  of  the  great  proteid 
molecules  are  composed  of  more  than  two  thousand  atoms. 
During  digestion  these  large  molecules  are  split  into  smaller 
molecules.  Each  molecule  of  starch  is  split  into  ten  molecules 
of  malt  sugar,  and  then  each  molecule  of  malt  sugar  is  split 

lies  practically  all  hygiene.  Additional  material  on  this  subject  is  given  in  the 
Appendix,  and  where  sufficient  time  is  given  to  the  subject,  this  material  should 
be  used. 


112  HUMAN  PHYSIOLOGY 

into  two  molecules  of  grape  sugar.  Thus  in  digestion,  starch, 
which  does  not  dissolve  in  water,  has  each  of  its  great  mole- 
cules split  up  into  twenty  molecules  of  grape  sugar,  which 
dissolves  and  passes  through  the  intestinal  wall.  The  great 
proteid  molecules  and  the  molecules  of  fat  are  also  split  in 
digestion  into  smaller  molecules  which  can  be  absorbed. 

How  the  Molecules  are  split  In  the  digestive  juices  are 
very  peculiar  substances  called  enzymes  or  ferments,  —  the 
ptyalin,  pepsin,  trypsin,  amylopsin,  and  steapsin  that  have  al- 
ready been  mentioned.  These  enzymes  have  the  power  of 
splitting  up  1  the  food  molecules.  Each  enzyme  can  split  the 
molecules  of  only  one  class  of  food,  so  there  must  be  different 
kinds  of  enzymes  for  digesting  the  carbohydrates,  the  pro- 
teids,  and  the  fats. 

Digestion  in  the  Mouth.  When  food  is  taken  into  the 
mouth,  the  salivary  glands  begin  to  work  more  rapidly,  and 
the  ptyalin  in  the  saliva  at  once  attacks  the  starch  and  begins 
to  change  it  to  malt  sugar.  At  the  best  there  is  not  much 
time  for  digestion  in  the  mouth,  and  by  eating  slowly  we  not 
only  give  the  ptyalin  more  time  to  work  on  the  starch,  but  we 
also  give  the  glands  more  time  to  secrete  the  ptyalin,  and 
we  mix  the  ptyalin  more  thoroughly  with  the  food.  All  this 
increases  starch  digestion  in  the  mouth. 

Digestion  in  the  Stomach.  The  food  remains  in  the  stom- 
ach from  one  to  four  hours.  The  main  digestion  carried 
on  here  is  that  of  the  proteids  by  the  pepsin  of  the  gastric 
juice.  This  enzyme  splits  the  proteid  molecules  into  smaller 
molecules  called  peptones,  which  dissolve  in  the  gastric 

1  Enzymes  are  found  only  in  living  animals  and  plants,  but  they  can  work 
outside  of  a  living  body  as  well  as  in  it.  If  ptyalin  is  put  into  a  dish  with  starch, 
or  pepsin  with  a  proteid,  digestion  will  go  on  in  the  dish  as  it  does  in  the  alimen- 
tary canal. 


DIGESTION,  ABSORPTION,  AND   OXIDATION       113 

juice.  The  stomach  keeps  working  the  food  along,  and  espe- 
cially in  its  lower  part  keeps  mixing  the  gastric  juice  with  it. 
After  about  an  hour  the  pylorus  opens  and  lets  the  more 
liquid  part  of  the  food  pass  on  into  the  intestine.  The  pepsin 
continues  its  work  on  the  food  remaining  in  the  stomach, 
and  as  this  is  sufficiently  digested,  it  is  passed  on  from  time 
to  time  into  the  intestine.  The  acid  in  the  gastric  juice  stops 
the  action  of  the  ptyalin  on  the  starch,  but  in  the  upper  part 
of  ,the  stomach  the  acid  sometimes  takes  an  hour  to  work  all 
through  the  food.  There  is,  therefore,  considerable  starch 
digestion  by  the  ptyalin  after  the  food  leaves  the  mouth. 

Digestion  in  the  Small  Intestine.  When  the  food  passes 
into  the  small  intestine,  the  glands  of  the  intestine  secrete 
their  juices,  the  gall  bladder  contracts  and  sends  the  stored-up 
bile  into  the  intestine,  and  the  pancreas  begins  to  send  in  the 
pancreatic  juice  with  its  three  powerful  enzymes, — trypsin, 
amylopsin,  and  steapsin.  Then  the  following  enzymes  finish 
the  digestion  of  the  foods : 

Amylopsin  changes  the  starches  which  escape  the  ptyalin 
into  malt  sugar.  Then  each  molecule  of  malt  sugar,  and  also 
the  cane  sugar  (ordinary  sugar)  that  we  take  in  our  food,  is 
split  by  enzymes  in  the  intestinal  juice 1  into  grape  sugar. 
Thus  all  the  starches  and  sugar  are  finally  changed  by  diges- 
tion into  grape  sugar. 

Trypsin  digests  the  proteids  which  have  escaped  the  pepsin. 

Steapsin  digests  the  fats.  Bile  is  not  a  digestive  juice,  for 
it  contains  no  enzymes;  but  it  assists  in  destroying  the  acids2 

1  The  enzyme  that  digests  malt  sugar  is  called  maltase.     The  enzyme  that 
digests  cane  sugar  is  called  invertase. 

2  The  intestinal  and  pancreatic  enzymes,  like  the  ptyalin,  cannot  work  when 
strong  acids  are  present.     Both  the  bile  and  the  pancreatic  juice  contain  minerals 
that  unite  with  and  destroy  the  acid  of  the  gastric  juice. 


114  HUMAN  PHYSIOLOGY 


of  the  gastric  juice,  it  in  some  way  assists  the  steapsin  in  the 
digestion  of  the  fats,  and  it  greatly  hastens  the  absorption  of 
the  fats. 

Absorption.  The  liquids  and  the  digested  foods  in  the  ali- 
mentary canal  pass  through  the  wall  of  the  canal  into  the 
blood.  This  process  is  called  absorption  and  takes  place 
chiefly  from  the  small  intestine.  After  absorption  the  blood 
carries  the  foods  all  through  the  body,  and  each  cell  takes 
from  the  blood  the  food  that  it  needs. 

The  Foods  within  the  Cells.  A  part  of  the  proteid  food 
taken  into  a  cell  is  used  for  building  purposes.  The  remainder 
of  the  food  is  oxidized  (burned)  within  the  cell.  In  this 
process,  the  food  molecules  are  torn  down  and  the  atoms  that 
were  in  these  molecules  unite  with  atoms  of  oxygen  —  the  food 
molecules  are  destroyed  and  new  kinds  of  molecules  are 
formed.  Therefore,  in  the  oxidation  (burning)  of  the  foods 
within  the  cells,  the  foods  are  destroyed  and  new  substances  are 
formed.  These  substances  are  the  body  wastes.  You  must 
get  clearly  in  mind  that  the  same  materials  (atoms)  that  go 
into  the  cells  in  the  form  of  foods  come  out  of  the  cells  as 
wastes,  —  that  the  foods  are  changed  to  ivastes  within  the  cells. 

The  Body  Wastes.  When  sugar  and  fat  are  burned  in  the 
body,  the  waste  products  are  carbon  dioxid  and  water.  When 
proteid  foods  are  burned  or  when  the  protoplasm  of  the  cells 
breaks  down,  carbon  dioxid  and  water  are  given  off,  and  in 
addition  uric  acid  and  many  other  waste  products  are  formed. 
The  carbon  dioxid  and  the  proteid  wastes  are  poisonous  and 
pass  out  of  the  body  through  the  lungs  and  kidneys. 

What  a  Cell  gains  by  burning  Food.  If  the  foods  simply 
go  into  a  cell  and  then  come  out  again  as  wastes,  what  does 
a  cell  gain  by  taking  in  and  burning  food?  A  cell  gains 
energy  by  the  oxidation  of  the  foods. 


DIGESTION,   ABSORPTION,   AND    OXIDATION       115 


When  on  a  cold  day  you  put  coal  into  the  stove,  you  do  not 
care  anything  about  whether  or  not  there  is  coal  in  the  stove. 
What  you  are  interested  in  is  the  heat      t,  '. .,  .  .     •  _-.....  %..  .... 

that  you  will  get  when  the  coal  burns. 
So  when  a  cell  burns  food,  it  is  not 
profited  by  the  atoms  and  molecules 
of  the  food,  but  by  the  energy — the 
heat  and  strength  and  power  to  work 
— that  is  given  to  the  cell  by  the 
burning.  In  this  connection  it  would 
be  well  to  read  again  pages  78  and  79. 

The  Storage  of  Foods  in  the  Body. 
Our  cells  must  have  a  constant  sup- 
ply of  food,  and  it  is  necessary  to  FlG.  ^  The  foods  pass  into 

have  a  Store  of  food  in  the  body  that    a  cell  and  are  changed  to  wastes 

can  be  used  in  times  of  sickness  or  Wlthin  the  ceiu 
starvation.  When  sugar  is  abundant,  a  few  ounces  of  it  can 
be  stored  by  the  liver  until  it  is  needed  by  the  cells.  The 
great  store  of  food  in  the  body,  however,  is  in  the  form  of  fat. 
The  fat  is  deposited  about  the  intestines,  kidneys,  and  other 
internal  organs,  it  is  packed  among  the  muscles  and  in  other 
tissues,  and  a  layer  of  fat  is  laid  down  under  the  skin.  The 
fat  under  the  skin  is  useful  not  only  for  feeding  the  body  in 
times  of  food  scarcity,  but  to  retain  the  body  heat. 

Fat  in  Animals.  Animals  that  hibernate  go  into  their  win- 
ter quarters  fat  in  the  autumn,  use  up  their  fat  during  their 
winter's  sleep,  and  come  out  thin  in  the  spring.  The  camel 
has  a  store  of  fat  in  the  hump  on  its  back,  which  enables  it 
to  go  for  many  days  without  food.  Seals,  whales,  and  other 
warm-blooded  animals  that  live  in  cold  waters  have  a  thick 
layer  of  fat  under  the  skin  to  keep  in  the  body  heat.  In  a 
whale  this  layer  of  blubber  is  sometimes  two  feet  thick. 


Il6  HUMAN  PHYSIOLOGY 


ALCOHOL  AND   DIGESTION 

Alcoholic  Drinks  and  Digestion.  Alcohol  taken  with  food 
causes  an  increase  in  the  amount  of  saliva  and  gastric  juice 
secreted,  but  it  seriously  interferes  with  the  work  of  the  pepsin 
if  more  than  five  per  cent  of  the  contents  of  the  stomach  is 
alcohol.  Alcohol  also  checks  stomach  digestion  by  paralyzing 
the  muscles  of  the  stomach,  and  beer  and  wine  contain  acids 
and  other  substances  that  very  greatly  hinder  the  work  of  the 
ptyalin.  On  the  whole,  the  rate  of  proteid  digestion  is  not 
much  changed  by  alcoholic  drinks  in  small  quantities,  but 
the  digestion  of  the  starch  is  greatly  hindered.  The  whole 
question  of  the  effects  of  alcohol  on  the  process  of  digestion 
is  of  little  practical  importance,  however,  for  alcohol  so  fre- 
quently causes  diseases  of  the  digestive  organs  that  it  would 
be  unwise  to  take  it  into  the  alimentary  canal,  even  though 
it  greatly  aided  digestion. 

Effects  of  Alcohol  on  the  Work  of  the  Liver.  The  liver 
manufactures  bile  and  stores  up  sugar.  It  has  besides  a 
third  function,  one  connected  with  the  uric  acid  and  other 
proteid  wastes  of  the  body.  The  uric  acid  is  poisonous  to 
the  body,  and  if  it  is  not  removed  from  the  blood,  rheuma- 
tism, gout,  and  other  serious  troubles  follow.  The  liver 
changes  a  considerable  part  of  the  uric  acid  to  urea,  which  is 
taken  out  of  the  body  by  the  kidneys. 

Alcohol  not  only  produces  the  diseased  condition  of  the 
liver  so  commonly  found  in  alcohol  users  (page  102),  but  it 
sometimes  interferes  especially  with  the  manufacture  of  urea 
in  the  liver.  In  some  persons  alcohol  even  in  very  small 
amounts  (the  amount  that  one  would  get  in  a  glass  of  beer) 
seriously  hinders  the  liver  in  its  work  of  changing  uric  acid  to 


DIGESTION,   ABSORPTION,   AND   OXIDATION        117 

urea.  A  large  part  of  the  uric  acid  is  then  left  in  the  blood 
to  bring  about  its  evil  consequences. 

Summary.  Foods  are  digested,  or  split  by  enzymes,  to 
make  them  dissolve  and  pass  through  the  walls  of  the  alimen- 
tary canal. 

Starch  is  split  into  malt  sugar  by  ptyalin  in  the  mouth  and 
stomach  and  by  amylopsin  in  the  intestine.  The  malt  sugar 
and  the  sugar  that  we  eat  are  split  in  the  intestine  into 
grape  sugar.  This  grape  sugar  is  then  absorbed  and  carried 
to  the  liver,  where  it  is  stored  until  it  is  needed  by  the  cells. 
Within  the  cells  the  grape  sugar  is  burned,  and  water  and 
carbon  dioxid  come  out  of  the  cells  as  wastes.  The  cells 
obtain  energy  from  the  sugar. 

Proteids  are  split  into  peptones  by  pepsin  in  the  stomach 
and  by  trypsin  in  the  intestine.  They  furnish  energy  and 
building  material  to  the  cells,  and  are  broken  up  into  water, 
carbon  dioxid,  and  uric  acid,  and  into  a  number  of  other 
substances  which  contain  the  nitrogen  of  the  proteid  molecule. 

Fats  are  digested  in  the  small  intestine.  They  are  burned 
to  carbon  dioxid  and  water  in  the  cells,  to  which  they  give 
energy. 

After  digestion  the  foods  are  absorbed  and  carried  by 
the  blood  to  the  cells.  Within  a  cell,  part  of  the  proteid 
food  is  used  in  building  new  protoplasm  and  the  remainder 
of  the  food  is  oxidized.  In  this  process  the  food  molecules 
are  torn  down  and  new  substances  (the  body  wastes)  are 
formed  from  the  atoms  of  these  molecules.  By  the  oxidation 
of  foods  a  cell  gains  energy. 

Cells  must  have  a  constant  supply  of  food,  and  there  is  in 
the  body  a  great  store  of  fat  for  use  in  times  of  sickness  or 
when  food  cannot  be  obtained. 

Alcoholic  drinks  increase  secretion  but  hinder  the  action  of 


1 1 8  HUMAN'  PHYSIO  LOG  Y 

the  enzymes,  and  on  the  whole  make  the  process  of  digestion 
slower.  They  also  produce  serious  results  by  keeping  the 
liver  from  changing  uric  acid  to  urea. 

QUESTIONS 

xWhy  must  foods  be  digested ?\ What  is  digestion?  What  kind  of 
changes  do  the  food  molecules  undergo  during  digestion  ?  What  is 
an  enzyme?  Name  some  of  the  digestive  enzymes. 

What  enzyme  is  in  the  saliva  and  what  kind  of  food  is  digested  in 
the  mouth  ?  To  what  is  this  food  changed  ?  Give  three  reasons  for 
eating  slowly.  What  enzyme  is  in  the  stomach?  What  kind  of 
foods  are  digested  in  the  stomach?  To  what  are  they  changed? 
How  long  does  food  remain  in  the  stomach  ?  What  do  the  stomach 
muscles  do  during  this  time?  What  effect  has  the  acid  of  the 
stomach  on  the  ptyalin? 

What  digestive  juices  work  on  the  foods  in  the  small  intestine? 
Name  the  three  enzymes  in  the  pancreatic  juice.  What  does  the 
amylopsin  do?  To  what  are  all  the  starches  and  sugars  finally 
changed  in  digestion?  What  does  the  trypsin  do?  the  steapsin? 
What  is  the  function  of  the  bile  ? 

What  is  absorption?  NAVhere  are  the  foods  taken  after  absorption? 
In  what  way  does  a  cell  use  part  of  the  proteid  food?  What  is  done 
with  the  remainder  of  the  food  ?  What  is  oxidation  ?  What  happens 
to  the  food  molecules  during  oxidation?  What  becomes  of  the  atoms 
that  were  in  the  food  molecules? 

What  wastes  are  formed  when  sugar  and  fat  are  burned  within  the 
cell  ?  when  proteids  are  burned  in  the  cell  ?  Which  of  these  wastes 
are  poisonous?  How  do  they  leave  the  body?  What  does  a  cell 
gain  by  burning  food? 

Why  is  it  necessary  to  have  food  stored  in  the  body  ?  Where  is 
sugar  stored?  In  what  form  is  the  chief  store  of  food  in  the  body? 
Where  in  the  body  is  the  fat  deposited?  How  is  fat  used  by  animals 
that  sleep  through  the  winter?  Where  does  the  camel  have  a  store 


DIGESTION,  ABSORPTION,  AND   OXIDATION        119 

of  fat  and  why  does  it  need  this  fat?     Why  do  animals  <that  live  in 
cold  climates  need  a  layer  of  fat  on  the  body? 

What  effect  has  alcohol  on  the  secretion  of  saliva  and  gastric  juice? 
on  the  rate  of  digestion  of  proteids?  of  starch?  Why  is  it  unwise 
to  take  alcohol  into  the  alimentary  canal?  What  are  the  three  func- 
tions of  the  liver?  What  effect  has  alcohol  on  one  of  these  functions? 
What  diseases  are  caused  by  this  ? 


If  a  cell  had  fats  and  carbohydrates,  could  it  live  without  proteids? 
Why?  If  it  had  proteids  and  fats,  do  you  think  it  could  live  without 
carbohydrates,  or  if  it  had  proteids  and  carbohydrates,  could  it  live 
without  fats  ?  Give  a  reason  for  your  answer. 

A  man  had  trouble  in  digesting  fatty  food.  WThat  enzyme  was 
weak  in  his  digestive  juices? 

Malt  contains  an  enzyme  that  does  the  same  work  as  ptyalin  and 
amylopsin.  A  man  who  had  stomach  indigestion  took  malt  to  relieve 
the  difficulty.  What  mistake  did  he  make  ?  What  enzyme  should  he 
have  taken? 

Suppose  there  is  trouble  in  digesting  starch.  What  other  food  can 
be  eaten  that  will  give  the  cells  grape  sugar? 

What  enzyme  is  lacking  when  there  is  trouble  in  digesting  sugar,  or 
sweet  materials  like  candy  and  cake  that  contain  much  sugar?  Would 
the  use  of  malt  or  pepsin  relieve  the  trouble?  Is  it  possible  to  furnish 
the  cells  with  grape  sugar  without  eating  sugar  ?  How  ? 

What  enzymes  are  mainly  employed  in  digesting  the  following 
foods  :  potatoes  ;  maple  syrup  ;  butter  ;*  cheese  ;  beans  ;  lean  meat ; 
fat  meat? 

Find  out  what  enzymes  you  can  buy  in  a  drug  store.  Do  any  ani- 
mals have  enzymes  that  we  do  not  have?  Do  plants  have  enzymes? 


CHAPTER   X 

DIETETICS 

What  a  Food  is.  A  food  is  a  substance  that  can  be  di- 
gested; l  that  can  furnish  the  cells  with  either  building  material 
or  energy,  or  with  both  building  material  and  energy  ;  and  that 
does  not  injure  the  cells.  Coal  contains  energy,  and  dyna- 
mite contains  great  quantities  of  energy ;  but  the  diges- 
tive enzymes  cannot  split  the  molecules  of  coal  and  dynamite, 
so  these  substances  are  of  no  use  for  food.  Opium  can  be 
burned  in  the  cells,  and  of  course  must  furnish  heat  to  the 
cells.  Yet  opium  is  not  a  food  but  a  poison,  because  the 
injury  done  by  it  to  the  cells  is  many  times  greater  than 
the  good  done  by  the  little  energy  which  it  yields.  A  true 
food  not  only  must  furnish  energy,  but  also  must  not  injure 
the  cells. 

In  dietetics  we  have,  therefore,  two  problems.  For  our 
food  we  must  choose  substances  that  can  be  digested  without 
injury  to  the  digestive  organs^  and  substances  that  will  supply 
the  needs  of  the  body  ivithout  injuring  it. 

KEEPING  THE   DIGESTIVE   ORGANS  IN   HEALTH 

One  of  the  most  important  problems  connected  with  our 
diet  is  that  of  keeping  the  digestive  organs  in  health.  Not 
only  do  these  organs  get  out  of  order  easily,  but  digestive 

1  A  few  foods,  e.g.  grape  sugar,  and  some  of  the  ingredients  of  soups,  are  in 
such  a  form  when  eaten  that  they  can  be  absorbed  without  digestion.  These, 
of  course,  need  no  digestion. 

120 


DIETETICS  121 

troubles  are  exceedingly  stubborn  and  difficult  to  cure.  Below 
you  will  find  some  of  the  results  and  causes  of  indigestion. 

Results  of  Indigestion.  If  food  lies  in  the  stomach  for  a 
long  time  without  digestion,  too  much  acid  will  collect  in  the 
stomach.  Sometimes  the  stomach  becomes  so  sour  from 
these  acids  that  it  throws  its  contents  out  to  get  rid  of 
them.  Intestinal  indigestion  is  even  worse  than  stomach 
indigestion,  so  it  is  a  matter  of  great  importance  to  select 
food  that  can  be  digested  and  moved  along  the  alimentary 
canal  in  a  reasonable  time.  It  is  also  very  important  that 
the  undigested  remains  of  the  foods  be  cleared  out  of  the 
large  intestine  daily.  If  this  is  not  done,  bacteria  will  grow 
in  the  large  intestine  and  form  substances  that  are  very 
injurious1  to  the  body.  These  substances  will  then  be 
absorbed  and  carried  all  through  the  body  by  the  blood, 
causing  headaches  and  the  trouble  called  biliousness. 

Causes  of  Indigestion.  I .  Eating  too  rapidly  and  not  chew- 
ing the  food  into  fine  pieces.  It  is  exceedingly  important  that 
the  food  be  broken  into  fine  pieces,  so  that  the  saliva  will  be 
well  mixed  with  it,  and  so  that  the  enzymes  can  get  at  its 
molecules.  Large  pieces  of  food  not  only  remain  for  a  long 

1  The  importance  to  the  health  of  the  prompt  movement  of  the  food  along  the 
alimentary  canal  cannot  be  too  strongly  emphasized.  If  the  intestinal  muscles  are 
slow  in  their  work,  the  bacteria  that  are  always  present  in  the  alimentary  canal 
will  produce  offensive  gases  that  will  be  carried  to  the  lungs  and  given  off  in  the 
breath,  and  substances  that  will  poison  the  whole  body  will  be  absorbed  from  the 
intestine.  Nearly  all  headaches  are  due  either  to  the  eyes  or  to  these  substances, 
and  it  is  now  thought  that  some  of  the  very  serious  diseases  of  the  liver  and 
kidneys  are  due  to  these  same  poisons.  Coarse  vegetables,  fruits  (especially  if 
the  skins  are  eaten),  corn  meal,  oatmeal  and  whole  wheat  bread  furnish  consider- 
able amounts  of  indigestible  matter  which  stimulates  the  muscles  in  the  walls  of 
the  alimentary  canal,  and  causes  them  to  move  the  food  along.  Drinking  consid- 
erable quantities  of  water  (most  of  which  should  be  taken  between  meals)  also 
helps  to  keep  up  the  movement  of  the  food  in  the  alimentary  canal, 


122  HUMAN  PHYSIOLOGY 

time  in  the  stomach  and  small  intestine,  but  they  often  pass 
undigested  into  the  large  intestine  and  furnish  food  for  the 
injurious  bacteria  that  grow  there.  Washing  the  food  down 
with  water  is  a  bad  habit,  for  it  causes  the  food  to  be  swallowed 
before  it  is  thoroughly  chewed.  Bad  teeth  are  another  com- 
mon cause  of  serious  stomach  and  intestinal  indigestion. 
Why? 

2.  Eating  more  than  can  be  digested  in  a  reasonable  time. 
The  troubles  that  arise  from  allowing  food  to  lie  too  long  in 
the  alimentary  canal  have  already  been  discussed  (page  121). 

3.  Eating  an  entire  meal  of  one  kind  of  food.     When   this 
is  done,  all  the  work  is  thrown  on  one  enzyme.     Too  much 
fat  meat  may  give  the  steapsin  more  work  than  it  can  do, 
while  the  amylopsin  is  entirely  idle  because  no  starchy  food 
was  eaten.     Eating  a  great  amount  of  candy  at  one  time  gives 
the  sugar-digesting  enzyme  more  sugar  than  can  be  digested 
for  hours,  while  the  other  enzymes  have  nothing  to  do.     This 
has  exactly  the  same  effect  as  eating  too  much,  for  in  either 
case,  digestion  will  be  so  long  delayed  that  stomach  and  in- 
testinal troubles  will   follow.     School   children  often  injure 
their  digestive  organs  by  eating  such  foods  as  candy,  pickles, 
and  pastry.     Some  of  these  foods  are  injurious  because  they 
are  taken  in  too  great  quantities-,  and  some  are  indigestible 
and  injurious  in  any  quantity. 

4.  Eating  irregularly  and  between  meals.     After  digestion, 
the  glands  of  the  alimentary  canal  should  have  time  to  rest 
and  prepare  a  supply  of  enzymes  for  the  next  meal.     Eating 
between  meals  also  dulls  the  appetite  at  mealtime,  and  we 
have  already  seen  (page  100)  how  hunger  and  a  good  appetite 
assist  in  causing  an  abundant  flow  of  digestive  juices. 

5.  Iced  drinks.     Warm  soup  taken  at  the  beginning  of  a 
meal  warms  the  stomach  and  starts  the  flow  of  the  gastric 


DIETETICS  123 

juice.  Ice  water  and  iced  tea  taken  with  the  meals  chill  the 
stomach  and  hinder  the  secretion  of  the  gastric  juice.  Ice- 
cold  soda  fountain  drinks  are  decidedly  injurious  if  taken 
frequently  or  in  large  amounts,  and  cool  drinking  water  is 
more  healthful  than  water  that  is  ice-cold. 

6.  Unappetizing  and  poorly  cooked  food.     If  not  properly 
cooked,  some  foods  are  hard  to  digest  (page  128),  but  the 
greatest  evil  in  bad  cooking  is  that  the  food  is  not  pleasant 
to  the  taste,  and  the  digestive  juices  are  not  secreted  abun- 
dantly.    Jams,  jellies,  soups,  and  some  other  foods  contain 
little  nourishment,  and   are  important   chiefly  because  they 
make  it  possible  for  us  to  eat  with  a  relish  and  to  digest  large 
quantities  of  rather  tasteless  but  very  nourishing  foods  like 
bread. 

7.  Talking  and  thinking  about  unpleasant  tilings  at  meal- 
time.    This   interferes   with    the  secretion   of  the  digestive 
juices  (page  101). 

8.  Hard  exercise  or  study  immediately  before  or  after  eating. 
This  takes  the  blood  away  from  the  digestive  glands  when 
they  need  it  to  manufacture  the  digestive  juices. 

9.  Lack  of  exercise.     Any  one  who  does   not   exercise  is 
almost  certain  to  suffer  from  indigestion  (page  73). 

10.  Overwork  or  overs tudy.     Either  one  of  these  will  bring 
on  indigestion.     Probably  the  nervous  system  is  first  injured, 
and  the  trouble  with  the  digestive  organs  comes  from  a  lack 
of  proper  nervous  control. 

11.  Trouble    with    the    eyes.     Many    cases    of    headache 
and  stomach  trouble  are  cured  at  once  by  fitting  the  eyes 
with  proper   spectacles   or  eyeglasses.     Probably   bad   eye- 
sight,  like  overwork,  injures   the  nervous   system,  and  the 
nervous  system  then  fails  properly  to  regulate  the  digestive 
organs. 


124  HUMAN  PHYSIOLOGY 


AMOUNT  AND   KINDS  OF   FOOD   NEEDED 

Amount  of  Food  needed.  A  healthy  man  of  average  weight 
(154  pounds),  usually  eats  about  4  ounces  of  dry  proteid  food 
a  day.  Whether  he  works  or  not  this  amount  of  proteid 
is  eaten. 

In  addition  to  the  proteid  that  he  eats  for  building  material, 
a  man  must  have  food  for  energy.  The  amount  he  will  need 
for  this  depends  on  how  much  work  he  does  and  on  whether 
or  not  he  is  exposed  to  the  cold.  A  hard-working  man 
usually  eats  twice  as  much  as  a  man  who  does  light  work ; 
and  some  lumbermen,  who  were  doing  heavy  work  in  the 
Maine  woods  in  the  cold  of  winter,  were  found  to  be  eating 
more  than  three  times  as  much  as  is  needed  by  a  bookkeeper 
or  a  tailor  who  does  light  indoor  work. 

A  Mixed  Diet  Best.  Only  the  proteids  furnish  building 
materials,  but  any  kind  of  food  furnishes  energy.  A  man 
could  eat  nothing  but  proteid,  but  so  much  of  one  kind  of  food 
would  be  sure  to  cause  indigestion,  and  the  system  would  be 
overloaded  with  proteid  wastes  (page  114).  It  is  therefore 
better  to  take  only  enough  proteid  to  furnish  building  mate- 
rial and  to  use  carbohydrates  and  fats  for  energy  foods. 

Fats  give  more  than  twice  as  much  heat  as  the  carbo- 
hydrates give,  and  the  Eskimos  and  other  peoples  living  in 
cold  climates  eat  chiefly  proteid  and  the  fat  of  animals.  The 
people  of  warm  climates  live  principally  on  proteids  and  car- 
bohydrates, which  they  get  from  vegetables  and  fruits.  Pro- 
teids and  either  one  of  the  energy  foods  will  do,  but  it  is 
better  for  the  digestion  to  take  both  fats  and  carbohydrates. 
An  additional  reason  for  always  eating  some  fat  is  that  the 
body  seems  more  liable  to  certain  diseases,  among  them  con- 
sumption, if  the  amount  of  fat  in  the  diet  is  very  small. 


DIETETICS  12$ 

Mistakes  in  Diet  from  the  Standpoint  of  Health.  The  three 
most  common  mistakes  in  diet,  from  the  standpoint  of  health, 
are  eating  in  suck  a  way  as  to  cause  indigestion,  eating  either 
too  much  or  not  enough  proteid,  and  not  eating  enough  fat. 

The  vegetable  carbohydrates  are  the  cheapest  of  all  foods, 
and  among  the  very  poor,  families  sometimes  live  almost  en- 
tirely on  them  and  fail  to  get  enough  proteids  and  fats.  The 
poor  peasants  of  some  European  countries  who  live  chiefly 
on  potatoes  and  other  vegetables,  have  not  the  same  strength 
for  their  work  that  American  workmen  have  who  eat  meat, 
butter,  eggs,  and  wheat  bread,  in  addition  to  vegetables. 
On  the  other  hand,  the  proteids  are  the  most  appetizing  of 
all  the  foods,  and  among  the  wealthier  classes  too  much 
proteid  is  often  eaten.  The  old  English  gentlemen  used  to 
feast  largely  on  venison  and  beef,  and  this,  with  their  wine- 
drinking,  gave  them  gout,  rheumatism,  and  kidney  and  liver 
trouble.  Among  Americans,  the  two  most  common  mistakes 
in  diet  are  eating  too  much  or  too  little  proteids,  and  not 
eating  enough  fats. 

Mistakes  in  Diet  from  the  Standpoint  of  Economy.  In 
oysters  we  pay  over  $5  for  a  pound  of  proteid,  while  in 
bread  the  same  amount  of  proteid  can  be  bought  for  70 
cents.  If  a  man  has  a  good  appetite  and  strong  digestive 
organs,  and  only  a  little  money,  it  is  plain  that  he  had 
better  buy  his  proteids  in  bread,  and  not  in  oysters.  Also, 
in  beef  at  14  cents  a  pound  we  pay  more  than  three  times  as 
much  for  energy  as  we  pay  for  energy  in  potatoes  at  75  cents 
a  bushel.  It  is  therefore  cheaper  to  use  potatoes  for  energy 
food  than  the  more  expensive  proteid  foods  like  beef. 

Buying  foods  out  of  season  is  another  economic  mistake 
made  by  many  people.  A  box  of  strawberries  may  cost 
30  cents  at  the  beginning  of  the  season,  and  in  three  weeks 


126  HUMAN  PHYSIOLOGY 

it  may  be  possible  to  buy  three  boxes  for  30  cents.  If  a  per- 
son  has  not  a  great  deal  of  money  and  wants  strawberries, 
he  should  not  spend  30  cents  for  one  box,  but  should  wait 
until  he  can  get  three  boxes  for  30  cents.  Economy  in  buy- 
ing foods  is  an  important  matter,  for  the  average  family  is 
not  wealthy,  and  money  that  is  badly  needed  for  other  pur- 
poses is  often  spent  in  buying  foods  when  they  are  out  of 
season,  and  in  buying  expensive  foods  when  cheaper  foods 
would  do  as  well  from  the  standpoint  of  health. 

Following  a  Healthy  Appetite.  From  all  that  you  have 
now  learned  you  know  that  a  healthy  diet  must  contain  the 
proteids,  carbohydrates,  and  fats  in  such  proportions  that 
they  will  give  the  body  its  building  materials  and  energy,  and 
at  the  same  time  will  not  burden  it  with  proteid  wastes  or 
cause  trouble  in  the  alimentary  canal;  and  that  our  food  must 
be  properly  cooked  or  otherwise  prepared  to  make  it  appetiz- 
ing, or  it  will  not  be  digested. 

If  you  will  stop  to  consider,  you  will  see  that  in  following 
a  moderate,  healthy  appetite,  we  shall  very  likely  get  about 
the  things  that  we  need.  We  eat  lean  meat  to  give  us  proteid, 
and  bread  or  potatoes  with  it  to  furnish  carbohydrates.  We 
like  a  little  butter  with  our  bread,  and  that  gives  us  some  fat, 
and  if  we  have  no  fruit  or  fresh  vegetables  for  some  time,  we 
become  hungry  for  them.  When  the  body  needs  anything, 
the  appetite  will  usually  let  us  know. 

Yet  we  must  remember  that  some  individuals  have  an 
appetite  for  green  fruit  and  other  unhealthful  substances, 
and  that  other  persons  get  into  the  habit  of  eating  far  more 
of  certain  staple  foods,  especially  of  meats,  than  the  body 
needs.  The  appetite  can  be  followed  only  when  it  is  really 
a  healthy  appetite  and  calls  for  those  things  that  are  needed 
to  keep  the  body  in  health. 


DIETETICS  127 

Mistaken  Ideas  in  Regard  to  Foods.  Several  mistakes  in 
regard  to  foods  are  common  throughout  our  country.  One 
is  that  there  is  a  difference  between  vegetable  and  animal 
foods.  Animal  foods  usually  have  less  refuse  matter  in  them 
than  vegetable  foods,  and  are  often  more  easily  digested  ;  but 
there  is  no  reason  to  think  that  in  nourishing  the  body,  anima] 
food  differs  from  vegetable  food. 

Another  idea  that  has  no  foundation  in  truth  is  that  the 
cells  of  the  brain  require  different  food  from  the  other  cells 
of  the  body.  Still  another  is  that  certain  breakfast  foods 
made  from  grains  are  particularly  valuable  as  foods.  They 
contain  only  the  carbohydrates  and  proteids  that  were  in  the 
grain  from  which  they  were  made,  and  their  food  value  is 
about  the  same  as  the  food  value  of  an  equal  weight  of  bread. 
They  are  clean,  digestible,  and  nutritious  foods,  but  lack  the 
wonderful  properties  claimed  for  them  in  some  advertise- 
ments. 

Another  thing  long  believed  to  be  true  was  that  whole 
wheat  bread  is  more  valuable  than  ordinary  white  bread.  It 
is  true  that  whole  wheat  bread  contains  more  proteid  than 
the  bread  made  from  the  inner  part  of  the  grain,  but  it  is  not 
so  digestible ;  and  it  has  been  found  that  the  body  gets  more 
proteid  out  of  a  pound  of  white  bread  than  out  of  a  pound  of 
brown  bread.  Still  another  mistake  is  to  suppose  that  beef 
tea  is  very  nourishing.  In  reality  it  contains  almost  no  nutri- 
ment. It  is  appetizing  and  stimulating,  and  is  often  very 
valuable  to  a  sick  person  because  it  enables  him  to  take  and 
digest  other  food,  but  beef  tea  alone  should  not  be  depended 
on  for  nourishment  in  any  long-continued  illness. 

Another  idea  common  among  intelligent  people  is  that  we 
might  live  much  better  and  more  economically  if  we  would 
change  our  diet  and  eat  chiefly  nuts,  bananas,  beans,  or  some 


128 


HUMAN  PHYSIOLOGY 


other  article  not  commonly  used  as  one  of  our  main  foods. 
This  idea  does  not  seem  to  be  correct.  The  starch  in  bananas 
is  raw,  and  is  difficult  of  digestion.  Beans  are  very  rich  in 
proteid,  but  they  are  hard  to  digest,  and  if  eaten  in  large 
quantities,  disagree  with  many  people.  Nuts  are  also  diffi- 
cult to  digest  and  in  large  quantities  give  too  much  fat  for 
most  people.  Some  persons  keep  their  health  on  these  foods; 
but  man  has  been  testing  the  different  foods  for  thousands 
of  years,  and  long  ago  he  learned  which  ones  are  best  for 
the  average  person.  The  flesh  of  animals,  milk,  eggs,  grains, 
potatoes,  and  a  few  other  vegetables  make  up  the  bulk  of  the 
world's  food,  other  things  being  used  in  smaller  quantities. 

Cooking.     Cooking  makes  many  foods  more  appetizing,  and 
thus  causes  a  greater  flow  of  the  digestive  juices.     Cooking 

also  makes  many  foods  more  di- 
gestible. By  cooking,  vegetables 
and  the  connective  tissue  fibers 
of  meats  are  made  more  tender. 
This  causes  the  vegetables  and 
meats  to  fall  to  pieces  more 
easily,  and  the  digestive  juices 
are  thus  given  a  better  oppor- 
tunity to  do  their  work. 

Cooking  is  especially  impor- 
tant in  the  case  of  starchy  foods, 
because  raw  starch  is  in  hard  little 
grains  which  the  digestive  juices 
cannot  penetrate,  and  which  the 
enzymes  break  up  very  slowly.  Raw  starch,  therefore,  is 
almost  indigestible.  Cooking  the  starch  grains  causes  them 
to  soften,  swell,  and  burst.  The  enzymes  are  then  able  to  get 
in  among  the  starch  molecules  to  digest  them. 


FlG.  61.     Starch  grains  in  the  cells 
of  a  potato. 


DIETETICS 


129 


Frying.     Frying  is  not  a  healthful  way  to  cook  most  foods. 

Too  much  fat  in  the  stomach  hinders  the  secretion  of  the 

gastric  juice,  and  in  frying,  the  food  is  coated 

with  fat.     As  the  food  passes  through  the 

mouth    and  stomach    it   is  covered  with  a 

layer  of  fat,  and  this  coating  of  fat  is  not 

digested  off   until  the  intestine  is  reached. 

The  ptyalin  and  pepsin  are  thus  to  a  certain 

extent  shut  off  from  the  food  and  are  not 

able  to  do  their  work  properly. 

Dangers  from   Raw   Meats.     Pork  some- 
times contains  small  worms  called  trichina.1 

These  when  taken 
into  the  alimen- 
tary canal  pass 
into  the  body, 
enter  the  muscles, 
and  kill  the  mus- 
cle cells.  This 
disease  is  called  trichinosis. 

The  young  of  the  tapeworm  is 
found  in  both  pork  and  beef. 
When  taken  into  the  intestine  it 
fastens  itself  to  the  intestinal  wall 

FIG.  63.    Tapeworm.  fcy  small  hooks  Qn  .^  head>  absorbs 

the  digested   food  in  the  intestine,  and  grows  into  a  long 
worm.2 


FIG.  62.  A  trichina 
lying  among  the  mus- 
cle cells. 


1  An   ounce  of  pork   may  contain  80,000   trichinae.    Each   female  produces 
about  1000  eggs  in  the  intestine,  which  would  give  about  40,000,000  of  these 
small  worms  from  an  ounce  of  pork.    The  eggs  hatch  in  the  intestine  and  the  young 
bore  through  the  intestinal  wall,  enter  the  blood,  and  are  carried  to  the  muscles. 

2  Tapeworms  often  measure  several  feet,  and  sometimes  several  yards,  in  length. 


130  HUMAN  PHYSIOLOGY 

Meat,  especially  pork,  should  be  well  cooked  before  it  is 
eaten,  to  kill  any  parasites  that  may  be  in  it.  When  thick 
pieces  of  meat  are  fried,  the  inside  parts  may  not  be  suffi- 
ciently heated  to  kill  everything  in  the  meat,  but  boiling  or 
baking  renders  meat  absolutely  safe  from  parasites. 

Dangers  from  Bacteria  in  Foods.  In  later  chapters  we  shall 
take  up  the  subject  of  disease  germs  and  learn  how  the  germs 
of  typhoid  fever,  diphtheria,  and  other  dangerous  germs  are 
carried  in  foods.  It  is  well  for  you  to  understand  now,  how- 
ever, that  all  decay  is  due  to  bacteria,  and  that  as  most  foods 
form  a  splendid  breeding  place  for  bacteria,  they  therefore 
quickly  decay.  In  caring  for  foods,  cleanliness,  to  keep  germs 
from  getting  into  them,  and  cold,  to  keep  the  germs  from  grow- 
ing, are  the  two  most  important  points.  Any  food  that  is  at 
all  tainted  is  so  full  of  germs  that  it  is  unfit  for  use,  and  in 
general,  the  fresher  a  food  is  when  it  is  used,  the  fewer  germs 
it  has  in  it. 

Patent  Medicines.  Often  we  read,  in  advertisements,  of 
medicines  that  will  cure  cancer,  consumption,  dyspepsia,  and 
many  other  of  our  worst  ills.  These  medicines  will  not  do 
what  is  claimed  for  them.  If  there  were  any  medicines  that 
would  cure  cancer  or  consumption,  the  skillful  physicians 
and  scientists  who  are  at  the  heads  of  our  medical  colleges 
and  hospitals  would  know  it,  and  they  would  be  using  them 
and  telling  every  one  about  these  wonderful  remedies. 

Some  patent  medicines  contain  opium,  which  is  soothing 
and  causes  pain  to  be  unnoticed,  so  that  a  person  sometimes 
thinks  he  is  better  when  his  disease  has  not  been  affected  at 
all.  Other  patent  medicines  are  very  strong  in  alcohol,  —  as 
strong  as,  or  stronger  than,  the  most  powerful  alcoholic  drinks. 
A  dose  of  some  of  these  medicines  contains  enough  alcohol 
to  affect  the  body  decidedly,  and  the  strengthening  effect 


DIETETICS  131 

that  persons  sometimes  think  they  feel  when  they  use  these 
"tonics,"  is  nothing  but  the  effect  of  the  alcohol.  Many 
patent  medicines  of  course  contain  useful  drugs,  but  without 
the  advice  of  a  physician  it  is  unwise  to  take  in  among  the 
delicate  little  cells  of  our  bodies  any  strong  medicine  whose 
effects  we  do  not  understand. 


ALCOHOL  AS   A  FOOD 

The  question  is  often  asked  whether  or  not  alcohol  is  a 
food.  On  this  point  people  continually  disagree.  One  rea- 
son for  the  disagreement  is  that  different  definitions  for  the 
word  "  food  "  are  used.  A  food  is  often  defined  as  a  sub- 
stance which  can  be  burned  in  the  body  and  will  give  energy 
to  the  body.  In  this  sense,  alcohol  is  a  food,  for  in  moderate 
amounts  it  is  oxidized  in  the  body  and  gives  heat  and  strength 
to  the  muscles.  The  other  definition  of  a  food  is  that  given 
on  page  120.  This  definition  insists  that  a  food  not  only 
must  furnish  building  material  or  energy,  but  also  must  not 
injure  the  cells.  According  to  this  definition,  it  is  certain 
that  alcohol  in  any  but  very  small  quantities  is  not  a  food, 
for  it  works  great  harm  to  the  cells,  especially  to  the  nerve 
cells. 

Whether  or  not  alcohol  in  very  small  doses  injures  the 
cells,  is  very  uncertain.  If  you  took  a  drop  of  alcohol  into 
your  body,  its  effect  would  be  so  slight  that  you  could  not 
notice  it.  Even  if  it  injured  your  cells,  you  would  never 
know  it.  If  you  took  a  spoonful  of  alcohol,  probably  you 
still  could  not  notice  any  effect  on  yourself.  But  if  you 
began  the  habit  of  drinking  beer  or  wine  or  other  alcoholic 
drinks,  it  is  certain  that  you  would  get  enough  alcohol  to 
injure  your  body  decidedly.  We  do  not  discuss  whether 


132  HUMAN  PHYSIOLOGY 

a  very,  very  small  amount  of  a  poison  like  opium  or  bella- 
donna would  injure  the  cells,  and  whether  these  drugs  give 
energy  to  the  cells  and  are,  therefore,  foods.  There  is  little 
more  reason  for  discussing  whether  or  not  alcohol  is  a  food, 
for,  used  in  the  amounts  taken  by  any  one  who  drinks 
alcoholic  liquors,  it  is  not  a  food,  but  a  poison.  All  sensi- 
ble persons  know  that  men  do  not  drink  alcohol  because 
they  think  it  is  a  food,  and  that  the  question  of  whether 
alcohol  is  a  food  is  brought  up  to  find  an  excuse  and  not  a 
reason  for  drinking  it.  Professor  Bunge,  a  great  German 
physiologist,  chemist,  and  physician,  well  knew  this  and  said : 
"  There  is  never  any  lack  of  excuses  for  taking  a  drink. 
People  drink  when  they  meet ;  they  drink  when  they  part. 
They  drink  when  they  are  hungry  to  quiet  hunger;  they 
drink  when  they  are  surfeited  to  arouse  appetite.  They  drink 
when  it  is  cold  for  warmth ;  they  drink  when  it  is  hot  to  cool 
off.  They  drink  because  they  are  sleepy,  to  keep  awake ; 
they  drink  when  they  cannot  sleep,  to  induce  sleep.  They 
drink  because  they  are  sad ;  they  drink  because  they  are 
jolly.  They  drink  because  there  is  a  baptism;  they  drink 
because  there  is  a  burial ;  they  drink  and  they  drink." 

QUESTIONS 

What  is  a  food  ?  Why  cannot  coal  be  used  for  food  ?  opium  ? 
What  two  points  must  we  keep  in  mind  in  choosing  our  foods  ? 

Why  is  it  important  that  foods  be  digested  within  a  reasonable 
time  ?  Discuss  some  of  the  causes  of  indigestion. 

How  much  proteid  does  a  man  need  in  a  day  ?  On  what  does 
the  amount  of  other  food  that  a  man  needs  depend  ?  Why  would  it 
be  unwise  to  eat  only  proteid  foods  ?  Could  a  man  live  on  fats  and 
carbohydrates  ?  Why  ?  Could  he  live  on  proteids  and  carbohydrates  ? 
pn  proteids  and  fats  ?  Which  gives  more  energy,  fats  or  carbo- 


DIETETICS  133 

hydrates  ?  In  what  part  of  the  world  do  the  people  eat  more  carbo- 
hydrates? more  fats?  Is  it  better  to  eat  only  two  classes  of  food  or 
all  three  classes  ? 

Give  three  mistakes  made  in  diet,  from  the  standpoint  of  health. 
What  class  of  people  eat  too  little  proteid  ?  too  much  proteid  ?  Men- 
tion two  mistakes  from  the  standpoint  of  economy  that  are  made  in 
purchasing  foods.  What  is  said  about  following  a  healthy  appetite? 
Discuss  some  of  the  mistaken  ideas  that  are  held  in  regard  to  foods. 

Give  two  ways  in  which  cooking  assists  the  digestion.  What  effect 
has  cooking  on  meats  and  vegetables  ?  on  starch  ?  Why  is  frying 
an  unhealthful  method  of  cooking?  What  parasites  get  into  the  body 
from  meat?  How  may  these  parasites  be  killed? 

What  causes  decay  in  foods?  What  are  the  two  most  important 
points  in  caring  for  foods  ?  Why  are  fresh  foods  more  healthful  than 
foods  that  are  not  fresh? 

What  injurious  substances  do  some  patent  medicines  contain? 
Wrhy  is  it  not  advisable  to  take  medicine  without  the  advice  of  a 
physician?  What  two  definitions  are  sometimes  given  for  a  food? 
According  to  which  of  these  definitions  is  alcohol,  except  possibly  in 
the  very  smallest  quantities,  not  a  food?  Why  is  the  discussion  of 
whether  or  not  alcohol  is  a  food  of  little  practical  importance  ? 


A  pupil  had  for  lunch  lemon  pie,  cake,  candy,  and  olives.  What 
enzyme  would  do  most  of  the  work  in  digesting  this  lunch  ?  What 
important  food  elements  would  be  present  in  small  amounts  in  such  a 
lunch  ?  Is  it  safe  to  follow  an  appetite  that  calls  for  such  a.  lunch  ? 

A  pound  of  carbohydrates  is  a  fair  allowance  for  a  man  for  one 
day,  and  an  eight-year-old  boy  needs  about  half  as  much  food  as 
a  man.  A  boy  of  this  age  ate  his  dinner  and  then  bought  and  ate 
a  half  pound  of  candy.  What  enzyme  would  have  the  candy  to 
digest?  How  much  more  work  than  usual  do  you  suppose  the 
enzyme  had  that  afternoon?  Do  you  suppose  the  digestion  of  the 
sugar  was  finished  quickly  enough  to  avoid  trouble  in  the  alimentary 
canal  ? 


134  HUMAN  PHYSIOLOGY 


REVIEW  QUESTIONS 

\Chapter  VII.  Give  two  reasons  why  the  body  needs  food.  Of 
what  is  all  matter  composed?  Of  what  are  molecules  composed? 
What  is  an  element?  a  compound?  Name  the  three  classes  of 
foods.  Give  examples  of  foods  of  each  class.  How  do  these  food 
classes  differ  in  chemical  composition?  Mention  some  other  things 
that  are  necessary  to  the  body. 

Chapter  VIII. ^Explain  how  a  gland  is  formed  and  how  it  works. 
Draw  a  diagram  of  the  digestive  system  and  label  the  different  diges- 
tive organs.  \/What  is  the  function  of  the  stomach?  of  the  gastric 
juice?  How  long  is  the  small  intestine?  Name  three  secretions 
that  are  emptied  into  it.  Describe  the  villi.  What  is  their  function? 
Name  the  accessory  organs  of  digestion.  Define:  dentine;  enamel; 
pulp  cavity  ;  incisor ;  canine  ;  bicuspid  ;  molar. 

Name  and  locate  the  salivary  glands.  What  is  the  use  of  the 
saliva?  What  glands  of  the  digestive  system  are  known  to  be  affected 
by  the  nervous  system?  What  mental  condition  is  favorable  to  a 
good  digestion?  What  trouble  does  alcohol  cause  in  the  stomach? 
in  the  liver? 

Chapter  IX.^Vhy  must  food  be  digested?  How  are  the  food 
molecules  changed  in  digestion?  By  what  are  they  changed?  Tell 
where  the  following  enzymes  are  found,  and  what  food  each  one 
digests  :  ptyalin  ;  pepsin  ;  trypsin  ;  amylopsin  ;  steapsin.  To  what 
are  the  proteids  changed  in  digestion  ?  the  starches  and  sugars  ?  Why 
must  a  cell  have  proteid?  What  happens  to  the  food  molecules  when 
the  foods  are  oxidized  within  the  cells  ?  What  becomes  of  the  atoms 
that  were  in  the  food?  What  does  a  cell  gain  by  burning  food?  What 
use  is  the  fat  in  the  body  ?  What  effect  has  alcohol  on  digestion  ?  on 
the  work  of  the  liver? 

Chapter  X.  Define  a  food.  Give  some  causes  of  indigestion. 
How  much  proteid  is  needed  daily?  Why  is  a  mixed  diet  best? 
Mention  some  common  mistakes  in  diet ;  some  mistaken  ideas  in 
regard  to  foods.  How  does  cooking  assist  digestion?  How  does 
frying  make  some  foods  more  indigestible?  What  two  points  are 
important  in  caring  for  foods ?  Why  are  patent  medicines  dangerous? 
Why,  according  to  our  definition  of  a  food,  is  alcohol  not  a  food  ? 


CHAPTER   XI 

THE  CIRCULATORY  SYSTEM 

FROM  the  time  we  are  born  until  we  die,  the  heart  beats. 
Day  and  night  the  blood  flows  through  the  body,  passing  out 
from  the  heart,  streaming  in  among  the  cells,  and  hastening 
back  to  the  heart.  If  because  of  disease  or  injury  to  the 
body  the  heart  stops,  the  body  dies.  If  the  blood  is  weak 
and  thin,  the  health  of  the  body  suffers,  and  if  the  blood  is 
allowed  to  escape  from  the  body,  life  at  once  ceases. 

Why  does  the  heart  beat  ?  Why  is  the  blood  kept  flowing 
through  the  body  ?  How  does  it  help  the  cells  to  have  the 
blood  passing  by  them  ?  Why  are  physicians  so  anxious  that 
the  blood  be  kept  strong  and  pure  and  that  nothing  be  done 
that  will  injure  the  heart  ?  Why  could  not  the  body  continue 
to  live  even  though  the  heart  should  stop  beating  and  the 
blood  should  cease  to  flow  ?  To  answer  these  questions 
intelligently,  we  must  first  of  all  understand  the  great  laws 
according  to  which  the  body  lives.  Our  bodies  must  have 
food  and  ^vater,  they  must  have  oxygen,  they  must  get  rid  of 
their  poisonous  wastes,  and  they  must  have  an  even  tempera- 
ture, neither  too  hot  nor  too  cold.  Our  bodies  are  composed 
of  cells,  and  each  cell  must  have  all  of  these  things. 

The  Function  of  the  Blood.  The  human  body  is  a  great 
colony  of  cells.  The  food  and  water  for  all  the  cells  in  the 
colony  are  taken  in  through  the  alimentary  canal ;  but  there 
must  be  some  arrangement  so  that  a  cell  in  the  brain  or  in 


136  HUMAN  PHYSIOLOGY 

the  foot  can  get  the  food  that  has  been  prepared  for  it  by  the 
digestive  organs.  Oxygen  is  taken  in  through  the  lungs ; 
but  the  oxygen  must  be  distributed  all  through  the  body  to 
the  cells.  The  poisonous  wastes  leave  the  body  through  the 
lungs  and  kidneys ;  but  the  wastes  that  are  produced  in  the 
cells  must  be  moved  from  the  cells  to  the  lungs  and  kid- 
neys before  they  can  be  thrown  out  of  the  body.  The  heat 
of  the  body  is  produced  by  burning  food  within  the  cells ; 
but  in  certain  inner  parts  of  the  body,  like  the  liver  and 
muscles,  there  is  too  much  heat,  while  in  the  outer  parts  of 
the  body  there  is  not  enough  heat.  There  must,  therefore, 
be  some  way  of  distributing  the  body  heat  so  that  none  of 
the  cells  will  be  either  too  hot  or  too  cold. 

The  function  of  the  blood  is  to  carry  food,  water,  and  oxygen 
to  the  cells,  to  carry  ivastes  aivay  from  the  cells,  and  to  carry 
heat  from  the  warmer  to  the  cooler  parts  of  the  body.  As  the 
blood  flows  among  the  cells  it  feeds  them  and  gives  them 
oxygen,  picks  up  and  carries  away  their  wastes,  cools  the  hot 
cells,  and  warms  the  cells  that  are  too  cold.  The  body  may 
be  very  quickly  killed  by  stopping  the  flowing  of  the  blood 
among  the  cells. 

THE  CIRCULATORY  ORGANS 

The  flowing  of  the  blood  through  the  body  is  called  the 
circulation.  The  organs  concerned  in  keeping  up  the  circu- 
lation are  the  circulatory  organs.  These  are  the  heart  (Fig. 
70),  the  blood  vessels  (arteries,  veins,  and  capillaries),  and  the 
lymphatic  vessels  (Fig.  66). 

The  Heart  The  heart 1  is  usually  about  the  size  of  the 
closed  hand  of  the  person  to  whom  it  belongs.  It  lies  in  the 

1  The  heart  is  inclosed  in  a  double-walled  sac  called  the  pericardium.  (Fig. 
82.) 


THE  CIRCULATORY  SYSTEM  137 

thoracic  cavity  with  its  apex  (point)  to  the  left  of  the  center 
of  the  body.  The  walls  of  the  heart  are  composed  of  muscle 
cells,  and  within  the  heart  are  four  cavities,  —  two  upper 
cavities  called  auricles,  and  two  lower  cavities  called  ventri- 
cles. The  auricles  have  thin  walls,  for  their  task  is  the  small 
one  of  sending  the  blood  down  into  the  ventricles.  The  ventri- 

VENA    CAVA  DESCENDING    VENA    OAVA 


PULMONARY  ARTERY 


B 


FIG.  64.  Diagram  of  the  right  side  of  the  heart  showing  the  working  of  the  valves. 
When  the  ventricle  relaxes,  the  valves  are  as  shown  in  A.  When  the  ventricle  con- 
tracts, the  valves  are  as  shown  in  B. 

cles,  on  the  other  hand,  have  thick  walls  because  they  have 
the  heavy  work  of  forcing  the  blood  through  the  body.  The 
function  of  the  heart  is  to  keep  the  blood  circulating  through 
the  body. 

The  Action  of  the  Heart.  Place  your  hand  on  your  chest 
and  you  can  feel  the  heart  beat.1  What  is  it  doing  when  it 
beats  ?  It  is  pumping  the  blood  through  the  body. 

The  walls  of  the  auricles  first  contract  and  draw  inward  on 

1  When  the  ventricles  contract,  the  apex  of  the  heart  is  pressed  more  forcibly 
against  the  wall  of  the  chest.  This  causes  the  beat,  which  can  be  felt  by  placing 
the  hand  on  the  chest  over  the  heart.  The  pulse  that  is  felt  in  the  arteries  is  a 
wave  that  travels  out  in  the  blood  within  an  artery  when  the  ventricles  force  the 
blood  out  of  the  heart. 


CAPILLARIES  OF 
CHEST  AKD  ARMS 


DESCENDING  VENA  £AVA 
PULMONARY  ARTERY- 
RIGHT  LU 


CAPILLARIES  OF 

STOMACH,  INTESTINE 

AND    SPLEEN 


CAPILLARIES 
OF    HEAD 


LEFT  AURICLE 
LEFT  VENTRICLE 


DESCENDING 
AORTA 


CAPILLARIES 
OF   LEGS 


FlG.  65.     Diagram  of  the  circulation  of  the  blood  in  the  body. 
138 


LYMPHATIC    VESSEL 


THORACIC    DUCT 


LYMPHATIC    VESSEL 
FROM    INTESTINE 


FIG.  66.    The  heart  and  the  principal  vessels  of  the  body. 
139 


140 


HUMAN  PHYSIOLOGY 


the  blood,  forcing  the  blood  into  the  ventricles.  The  auricles 
then  relax  and  the  powerful  walls  of  the  ventricles  contract, 
squeezing  the  blood  out  into  the  arteries.  The  ventricles 
now  relax  and  for  a  moment  the  heart  rests.  Then  the 
auricles  again  contract,  completing  the  filling  of  the  ventricles; 
the  ventricles  squeeze  the  blood  out  into  the  arteries,  and  so 
the  process  is  repeated  again  and  again.  In  one  day  the  heart 
does  as  much  work  in  sending  the  blood  through  the  body  as 
its  owner  would  do  in  walking  eight  and  one  half  miles  on  a 
level  road. 


FIG.  67.  These  gates  work  like  the  valves  of  the  heart.  When  the  boy  pushes  on 
them  one  way,  they  open,  but  when  he  pushes  on  them  the  other  way,  the  chains  hold 
them  so  that  they  will  not  open. 

The  Rate  of  the  Heart  Beat.  In  an  adult  the  heart  usually 
beats  from  seventy  to  eighty  times  a  minute.  It  is  faster  in 
women  than  in  men,  and  varies  in  different  individuals,  some 
persons  naturally  having  a  faster  heart  beat  than  others. 
The  rate  of  the  heart  beat  varies  also  with  age,1  with  rest  and 
exercise,  and  with  health  and  disease.  You  should  count 
your  own  heart  beat  several  times  so  that  you  will  know  its 
average  rate.  Then  in  sickness  you  will  know  how  much  it 
varies  from  its  natural  beat. 

1  The  heart  beat  at  different  ages  is  about  as  follows:  at  birth,  130-140;  first 
year,  115-130;  second  year,  100-115;  third  year,  90-100;  seventh  year,  85-90; 
fourteenth  year,  80-85;  adult  life,  70-80;  old  age,  60-70;  extreme  old  age, 
75-80. 


THE   CIRCULATORY  SYSTEM  141 

The  Valves  of  the  Heart.  .In  the  heart  are  four  valves, 
two  between  the  auricles  and  the  ventricles  (Fig.  64),  and  two 
at  the  openings  of  the  great  arteries  (aorta  and  pulmonary 
artery),  which  lead  out  from  the  ventricles.  All  four  valves 
are  made  of  connective  tissue,  and  their  function  is  to  keep  the 
blood  from  flowing  backward. 

The  valves  between  the  auricles  and  ventricles  work  like 
little  doors  (Fig.  67)  which  open  only  downward  into  the 
ventricles.  Little  ligaments  hold  the  valves  so  that  they 
cannot  be  pushed  upward  into  the  auricles.  The  blood  can 
therefore  flow  from  the  auricles  into  the  ventricles,  but 
when  the  ventricles  contract,  the  blood  pushes  up  under 
the  valves  and  lifts  them  so  that  the  openings  between  the 
auricles  and  ventricles  are  closed.  Since  the  blood  cannot 
pass  back  into  the  auricles,  it  must  flow  out  into  the  arteries 
when  the  ventricle  walls  contract. 

Each  of  the  valves  at  the  entrance 
to  the  great  arteries  is  made  of  three 
loose  pockets  on  the  wall  of  the 
artery.  The  pockets  open  upward, 
and  as  the  blood  leaves  the  ventricles 
it  readily  flows  over  them.  But  when 
the  ventricles  relax  and  the  blood 
starts  to  run  back  into  the  heart,  the  FIG.  68.  The  base  of  the  aorta 
pockets  fill  with  blood  and  hang  out  in  ^V^? starts  Tflow 

the  Opening  of  the  artery  SO  that  they    backward  into  the  heart  it  catches 

touch  each  other.     They  thus  close  in  the  pockets,  which  then  swing 

out  and  close  the  opening  in  the 

the  passageway  and  keep  the  blood  aorta.   See  also  Figure  64. 
from  flowing  back  into  the  heart. 

Blood  Vessels.  Arteries  are  blood  vessels  in  which 
the  blood  flows  away  from  the  heart  Veins  are  blood 
vessels,  in  which  the  blood  flows  to  the  heart.  Capillaries 


142  HUMAN  PHYSIOLOGY 

are  small  vessels  through  which  the  blood  flows  from  tJie 
arteries  to  the  veins.1  The  two  great  arteries  (aorta  and 
pulmonary  artery)  that  leave  the  heart  divide  into  smaller 
arteries.  These  smaller  arteries  divide  again  and  again, 
until  finally  they  end  in  exceedingly  small  capillaries,  which 


FIG.  69.     The  blood  Rows  from  the  arteries  through  the  capillaries  into  the  veins. 

are  everywhere  among  the  cells.  After  running  in  among 
the  cells  the  capillaries  begin  to  unite.  More  and  more 
of  them  flow  together  and  form  small  veins.  The  small 
veins  continue  to  unite  and  form  larger  veins  until  they 
are  joined  into  the  large  veins,  the  vetuz  cavce  and  the 
pulmonary  veins ,  which  empty  into  the  heart  (Fig.  65).  You 
must  clearly  understand  that  in  the  circulation  the  blood  does 
not  get  out  of  the  blood  vessels,  but  passes  through  the  capil- 

1  To  THE  TEACHER:  If  a  microscope  can  be  procured,  the  teacher  should 
not  fail  to  have  his  pupils  observe  the  fascinating  sight  of  the  blood  corpuscles 
shooting  along  in  the  capillaries.  One  of  the  best  places  to  see  this  is  in  the 
tail  of  a  tadpole.  Lay  the  tadpole  on  a  flat  piece  of  glass,  and  it  will  usually 
become  quiet  enough  in  a  little  while  to  allow  the  microscope  to  be  focused  on 
the  capillaries. 


CIRCULATORY  SYSTEM 


143 


laries  from  the  arteries  to  the  veins  (Fig.  69).  So  abundant 
are  the  capillaries  that  the  finest  needle  thrust  into  the  body 
tissues  cuts  and  breaks  many  of  them. 


JUGULAR    VE 
(FROM    HEAD) 


SUBCLAVIAN   ARTERY 
(TO    ARM) 


SUBCLAVIAN    VEIN 
(FROM    ARM) 


DESCENDING    VE 


CAROTID    ARTERIES 
HEAD) 


RIGHT   VENTRICLE 


ASCENDING    VENA    CAVA 


SUBCLAVIAN    ARTERY 
(TO    ARM) 


JUGULAR    VEIN 
(FROM    HEAD) 


SUBCLAVIAN    VEIN 
(FROM    ARM) 


PULMONARY   ARTERY 
LEFT  VENTRICLE 


DESCENDING     AORTA 


FIG.  70.     The  heart  and  the  bases  of  the  great  vessels. 

The  Walls  of  the  Blood  Vessels.  The  walls  of  the  arteries 
are  composed  chiefly  of  connective  tissue  and  of  muscle 
fibers  which  are  placed  circularly  about  the  vessels.  When 
the  muscle  fibers  in  the  wall  of  an  artery  contract,  they  make 
the  opening  of  the  artery  smaller,  and  a  less  amount  of 
blood  passes  through  it.  By  changing  the  size  of  the 


144  HUMAN  PHYSIOLOGY 

arteries,  some  of  the  blood1  can  be  cut  off  from  a  part  of  the 
body  that  is  resting  and  needs  only  a  little  blood,  and  can  be 
sent  to  a  part  of  the  body  that  is  working  and  needs  a  larger 
blood  supply. 

The  walls  of  the  veins  are  thinner  than  the  walls  of  the 
arteries,  and  have  in  them  more  connective  tissue  and  less 
muscle.  The  walls  of  the  capillaries  are  very  thin,  con- 
sisting of  only  one  layer  of  thin  flat  cells  and  a  few  fibers  of 
connective  tissue. 

The  Course  of  the  Circulation.  The  heart  is  a  double  organ. 
The  right  ventricle  sends  the  blood  through  the  lungs  to  the 
left  auricle.  The  left  ventricle  sends  the  blood  through  the 
body  to  the  right  auricle.  In  a  complete  circulation  the  blood 
therefore  passes  twice  through  the  heart.  By  studying  the 
diagram  on  page  138,  you  will  find  that  the  course  of  the 
blood,  beginning  with  the  right  auricle,  is  as  follows  : 

From  two  great  veins  (the  venae  cavse)  into  the  right 
auricle. 

From  the  right  auricle  into  the  right  ventricle. 

From  the  right  ventricle  into  the  pulmonary  artery  and  its 
branches. 

From  the  branches  of  the  pulmonary  artery  into  the 
capillaries  of  the  lungs. 

From  the  capillaries  of  the  lungs  into  four  pulmonary  veins. 

From  the  pulmonary  veins  into  the  left  auricle. 

From  the  left  auricle  into  the  left  ventricle. 

From  the  left  ventricle  into  the  aorta  and  its  branches. 

From  the  branches  of  the  aorta  into  the  capillaries  of 
the  body. 

1  It  is  estimated  that  the  capillaries  of  the  intestine  can  hold  all  the  blood  in 
the  body,  and  that  if  all  the  vessels  in  the  body  should  relax  at  one  time,  it  would 
take  several  times  as  much  blood  as  there  is  in  the  body  to  fill  all  of  them. 


THE  CIRCULATORY  SYSTEM  145 

From  the  capillaries  of  the  body  into  the  smaller  veins. 

From  the  smaller  veins  into  the  two  great  veins1  called  the 
ascending  and  descending  venae  cavae,  and  then  back  into 
the  right  auricle. 

Day  and  night  the  blood  circulates  through  the  body,  pass- 
ing out  from  the  heart  through  the  arteries,  flowing  through 
the  capillaries  and  returning  to  the  heart  by  way  of  the  veins. 
Day  and  night  the  heart  pumps  away,2  keeping  the  current 
of  blood  flowing  through  the  vessels.  No  other  organ  of  the 
body  is  so  hard-worked  as  the  heart,  which  pauses  to  rest 
only  between  its  beats. 

The  Nervous  Control  of  the  Circulation.  The  heart  has  two 
sets  of  nerves,  —  one  set  quickening  its  beat  and  the  other 
set  causing  it  to  beat  more  slowly.  Through  these  nerves, 
the  rate  of  the  heart  beat  is  controlled. 

The  muscles  in  the  walls  of  the  arteries  are  also  supplied 
with  two  sets  of  nerves.  One  set  of  nerves  causes  the 
muscles  in  the  arterial  walls  to  contract,  and  one  set  causes 

1  From  the  diagram  on  page  138  it  can  be  seen  that  the  portal  circulation,  or 
the  circulation  through  the  liver,  is  peculiar  in  that  the  blood  passes  through  two 
sets  of  capillaries.  The  blood  that  has  passed  through  the  capillaries  of  the 
stomach,  intestine,  pancreas,  and  spleen  is  collected  into  one  great  vein  (the 
portal  vein)  and  taken  to  the  liver,  where  it  again  spreads  out  in  the  capillaries 
among  the  liver  cells.  It  is  then  collected  into  the  hepatic  vein  and  goes  on 
to  the  heart.  Sugar  is  stored  in  the  liver,  and  the  advantage  of  this  arrange- 
ment is  that  the  blood  carrying  the  absorbed  sugar  passes  through  the  liver 
before  it  goes  to  the  rest  of  the  body.  The  blood  that  comes  to  the  liver  through 
the  portal  vein  has  lost  its  oxygen  in  the  first  set  of  capillaries,  so  the  liver  has 
another  supply  of  blood  coming  to  it  through  the  hepatic  artery  (page  138)  to 
furnish  it  with  oxygen. 

2  The  circulation  time  of  the  blood  through  the  body  (from  left  ventricle  to 
right  auricle)  is  on  an  average  something  like  a  minute.  The  circulation  time 
through  the  lungs  (from  right  ventricle  to  left  auricle)  is  about  twelve  or  fifteen 
seconds.  This  means  that  twice  in  every  minute  and  a  quarter  the  heart  must 
pump  all  the  blood  in  the  body  through  itself. 


146  HUMAN  PHYSIOLOGY 

them  to  relax.  The  size  of  the  openings  in  the  arteries, 
and  the  amount  of  blood  going  to  the  different  parts  of  the 
body,  can  thus  be  regulated  by  the  nervous  system. 
When  a  person  blushes,  the  little  arteries  in  the  skin  of  the 


FIG.  71.    The  vessels  of  the  foot.    Only  a  few  of  the  arteries  are  shown. 

face  open  and  allow  a  larger  quantity  of  blood  to  come  into 
them.  From  this  you  can  understand  how  quickly  the  size 
of  the  arteries  can  be  changed,  and,  when  you  think  of  the 
cause  of  blushing,  you  will  know  that  the  muscles  in  the 
blood  vessels  can  be  affected  by  the  nervous  system. 


THE  BLOOD   AND   LYMPH 

The  blood  makes  up  about  one  nineteenth  of  the  body 
weight.  It  is  composed  of  a  liquid  part,  the  plasma,  and 
of  red  and  white  blood  corpuscles  that  float  in  the  plasma. 
About  five  million  red  corpuscles  and  ten  thousand  white 
corpuscles  are  found  in  a  drop  of  blood.  There  are,  there- 


THE  CIRCULATORY  SYSTEM  147 

fore,  about   five   hundred  red  corpuscles  to  one  white  cor- 
puscle. 

The  Plasma.  The  blood  plasma  is  composed  mainly  of 
water.  Dissolved  in  the  plasma  are  the  different  foods,  salts, 
and  other  materials  used  by  the  cells.  ,-r;:~--v 
T lie  function  of  the  plasma  is  to  carry 
foods  and  wastes,  and  to  form  a 
liquid  in  which  the  corpuscles  can  float 
about  in  the  blood  vessels. 

The  White  Corpuscles.  The  white 
corpuscles  can  change  their  shape. 
They  are  the  only  cells  of  the  body, 
except  the  muscle  cells,  that  have 
the  power  of  movement,1  and  more  FlG"  72'  ^d  and  white  blood 

corpuscles. 

than  any  other  of  our  cells  they  re- 
semble the  little  one-celled  animals  about  which  we  studied  in 
the  first  chapter.  They  often  escape  from  the  capillaries 
by  passing  through  between  the  cells  of  the  capillary  wall 
(Fig.  73).  For  a  long  time  it  was  thought  that  the  white 
corpuscles  had  no  definite  work  to  do,  but  roamed  about 
while  the  other  cells  were  busy,  each  at  its  particular 
task.  Now  it  is  known  that  the  function  of  the  white  cor- 
puscles is  to  kill  tJie  disease  germs  which  get  into  the  body 
among  the  cells  (Fig.  137). 

The  Red  Corpuscles.  The  red  corpuscles  are  small,  cir- 
cular disks  with  a  hollow  in  each  side,  as  you  see  in  Figure  72. 
Most  of  them  are  formed  in  the  marrow  of  the  spongy  bone 
(page  42).  Here  some  of  the  cells  lose  their  nuclei,  take 
on  the  shape  of  corpuscles,  and  by  and  by  float  away  in 
the  blood  stream  as  red  corpuscles.  For  some  time  they 
circulate  through  the  blood  vessels,  but  finally  die  and 

1  On  ciliated  cells  (Fig.  6)   the  cilia  move,  but  the  cells  as  a  whole  do  not. 


148 


HUMAN  PHYSIOLOGY 


are  broken  up,  chiefly  in  the  spleen.  Part  of  the  broken 
down  materials  of  the  red  corpuscles  leave 
the  body  as  the  coloring  matter  of  the 
bile.  It  is  estimated  that  ^very  day 
about  fourteen  billions  of  red  corpuscles 
die  in  the  body,  and  as  many  new  ones 
are  formed. 

The  Function  of  the  Red  Corpuscles. 
The  function  of  the  red  corpuscles  is  to 
carry  oxygen  and  to  assist  tJie  plasma  in 
carrying  carbon  dioxid.  The  way  in  which 
the  red  corpuscles  carry  oxygen  is  very 
interesting.  They  have  within  them  a 
substance  called  hemoglobin.  When  this 
is  exposed  to  oxygen,  as  it  is  in  the  lungs, 
each  molecule  of  the  hemoglobin  unites 
with  a  molecule  of  oxygen  and  carries  the 
oxygen  away  with  it.  Then,  when  the 
corpuscle  goes  out  in  the  capillaries  among 
the  cells,  the  hemoglobin  :  gives  up  its  oxy- 
gen to  the  cells  (Fig.  74). 

The  carbon  dioxid  is  dissolved  in  both 
the  plasma  and   the  corpuscles.     It   does 
not,  however,  unite  to  any  extent  with  the 
FIG.  73.  A  white  cor-    hemoglobin  of  the  corpuscles,  as  the  oxy- 

puscle  escaping  from  a 


capillary. 


gen  does,  and  a  corpuscle  can  carry  both 


1  The  way  the  oxygen  is  carried  in  the  blood  may  be  represented  by  compar- 
ing the  blood  to  a  stream,  the  red  corpuscles  to  little  boats  in  the  stream,  and 
the  hemoglobin  molecules  to  little  jars  in  the  boat.  In  the  lungs  a  molecule  of 
oxygen  is  placed  in  each  of  the  jars  ;  out  in  the  capillaries  of  the  body  the 
oxygen  is  emptied  out  of  the  jars,  and  the  little  boat  floats  around  to  the  lungs, 
where  each  jar  is  again  loaded  with  a  molecule  of  oxygen. 


THE   CIRCULATORY  SYSTEM  149 

carbon  dioxid  and  oxygen  at  the  same  time.1  The  carbon 
dioxid  injures  the  cells  because  it  is  itself  poisonous,  and 
not  by  keeping  the  corpuscles  from  carrying  oxygen  to 
them. 

The  Color  of  the  Blood.  Blood  containing  oxygen  is  bright 
red  in  color,  and  blood  without  oxygen  is  dark,  appearing 
blue  in  the  veins  under  the  skin.  This  you  can  see  by  look- 
ing at  the  veins  in  your  forearm,  which  bring  the  blood  from 
the  hand  back  to  the  heart.  The  blood  gets  its  oxygen  in  the 
lungs  (Fig.  81)  and  loses  it  in  the  capillaries  of  the  body.  The 
blood  is  therefore  red  in  the  pulmonary  veins,  in  the  left  side 
of  the  heart,  and  in  the  aorta  and  all  its  branches.  It  is 
dark  in  the  veins  bringing  the  blood  from  the  body  to  the 
heart,  in  the  right  side  of  the  heart,  and  in  the  pulmonary 
artery.  The  same  thing  can  be  said  more  briefly  thus :  The 
blood  is  red  while  going  from  the  lungs  to  the  body  capil- 
laries, and  dark  while  going  to  the  lungs  from  the  body 
capillaries. 

The  Lymph.  The  blood  plasma  soaks  through  the  thin 
walls  of  the  capillaries  and  passes  out  among  the  body  cells. 
After  the  plasma  gets  outside  the  capillaries  it  is  called 
lymph.  The  lymph  surrounds  all  the  cells  in  the  body  and 
fills  all  the  little  spaces  between  the  cells.  A  fresh  supply 
of  lymph  is  constantly  escaping  from  the  blood,  and  the 
amount  of  lymph  in  the  body  is  several  times  as  great  as  the 
amount  of  blood. 

The  Function  of  the  Lymph.  The  function  of  the  lymph  is 
to  receive  food  and  oxygen  from  the  blood  and  pass  them  on  to 
the  cells,  and  to  receive  the  wastes  from  tJie  cells  and  pass  them 

1  In  suffocation  from  gas,  death  is  usually  caused  by  a  gas  called  carbon  mon- 
oxid  (CO).  This  unites  very  firmly  with  the  hemoglobin,  and  when  the  blood 
comes  to  the  lungs,  the  corpuscles  cannot  take  up  the  oxygen. 


HUMAN  PHYSIOLOGY 


FIG.  74.  As  the  blood  flows  through  the  capillaries 
it  gives  food  and  oxygen  to  the  cells  and  takes  wastes 
from  the  cells.  The  lymph  acts  as  a  middleman  be- 
tween the  cells  and  the  blood. 


to  the  blood.  The  cells  of  the  body,  except  the  blood  corpus- 
cles, lie  outside  the 
blood  capillaries. 
The  food  and  oxy- 
gen must  pass  out 
of  the  blood  capil- 
laries before  they 
can  reach  the  cells. 
This  the  food  and 
oxygen  do  by  pass- 
ing out  through  the 
capillary  walls  into 
the  lymph,  and  then 
through  the  lymph 
to  the  cells.  In 

the  same  way  the  wastes   reach  the  blood,  passing  out   of 

the   cells   into   the    lymph,  and   from  the 

lymph    into    the    blood.       The   lymph    is 

therefore   a   middleman    between    the   cells 

and  the  blood. 

The   Cells    in  the  Body   surrounded  by 

Liquid.     Each  cell  of  the  body  lives  in  a 

liquid  (the  lymph)  as  truly  as  does  a  little 

one-celled  animal  that  lives  in  a  pond  of 

water.     The    one-celled    animal   takes   its 

oxygen  and   food   from  the  water,  and  its       FIG  Muscle 

/-  wastes  pass  out  into  the  water.     The  cells     ceils   and  the  blood 
]  of  the  body  take  their  food  and  oxygen     capillaries  that  nourish 

I  them.    These  cells  are 

from  the  lymph,  and  discharge  their  wastes     surrounded  by  lymph 
into  it.     In  the  pond,  however,  there  is  an     as  are  the  ceils  in  Figure 
abundance   of   food   and    oxygen    for  the     74- 
little  animal,  and  the  amount  of  water  in  the  pond  is  so  great 


THE   CIRCULATORY  SYSTEM 


that  the  wastes  have  little  effect  on  its  purity.  In  the 
body,  on  the  other  hand,  the  cells  are  so  closely  crowded 
that  they  would  in  a  very  short  time  use  all  the  food  and 
oxygen  in  the  lymph,  and  fill  it  with  poisonous  wastes. 
There  must  therefore  be  some  way  of  constantly  sending  into 
the  lymph  a  fresh  supply  of  food  arid  oxygen,  and  of  con- 
stantly carrying  away  the  wastes;  and  this,  as  we  have  seen, 
is  done  by  the  blood. 


BLOOD 
PILLARY 


-MUCOUS 
CELL 


THE   LYMPHATIC   SYSTEM 

Since  the  plasma  is  continually 
escaping  from  the  blood  capillaries, 
there  must  be  some  way  of  carrying 
the  lymph  away  from  among  the 
cells;  otherwise  too  much  lymph 
would  collect  in  the  tissues  and  the 
body  would  become  swollen  with 
liquid.1  The  lymph  cannot  go  back 
into  the  blood  capillaries  against  the 
current  of  escaping  plasma,  so  there 
is  another  system  of  vessels  (Fig.  78) 
to  drain  it  away  from  among  the 
cells.  The  vessels  that  do  this  are 
called  the  lymphatic  vessels,  and  their 
function  is  to  collect  the  lymph  from 
among  the  tissues  and  carry  it  again 
to  the  blood. 

The     Lymphatic    Vessels.       The 

i  in  j_i  1  1_  *1  r  lli.     7O.       J\     vmub     ciiiu     us 

lymph  flows  into  the  lymph  capil-    yesseis  7The  ]ymphatic  vessels 
laries,  which  form  a  thick  network    (lacteais)  are  in  black. 


FIG.    76.      A    villus    and    its 


1  In  dropsy  the  lymph  collects  in  the  tissues  and  causes  great  swelling. 


152 


HUMAN  PHYSIOLOGY 


among  the  cells.  The  capillaries  unite  and  form  larger 
vessels,  which  finally  empty  the  lymph  back  into  the  blood. 
The  lymphatic  vessels  from  the  right  arm  and  the  upper 
part  of  the  right  side  of  the  body  empty  into  a  vein  in 
the  right  shoulder  (Fig.  66).  The  lymphatic  vessels  of  the 
remainder  of  the  body  empty  into  the  thoracic  duct.  This 


mCOMING    LYMPHATIC    VESSELS 


CORPUSCLES 
CONNECTIVE  TISSUE   CAPSULE 


FIG.  77.    A  lymph  node.    The  lymph  filters  through  among  the  white  corpuscles  in 

the  node. 


vessel  is  about  the  size  of  a  slate  pencil  and  runs  up  the 
back  of  the  ventral  cavity,  bending  over  at  the  top,  and  empty- 
ing into  a  large  vein  deep  in  the  left  shoulder.  Thus  the 
lymph  that  escapes  from  the  blood  capillaries  is  taken  up  by 
the  lymphatic  vessels  and  brought  back  to  the  blood. 

The  Lymphatics  of  the  Small  Intestine.  Besides  taking 
up  the  escaped  plasma  from  among  the  cells,  the  lymphatic 
vessels l  in  the  small  intestine  do  another  work.  The  digested 
foods  —  sugars,  proteids,  and  fats  —  all  pass  through  the 
walls  of  the  villi  (page  93),  but  to  get  into  the  blood  the  fats 

1  The  lymphatics  of  the  small  intestine  are  called  lacteah. 


THE  CIRCULATORY  SYSTEM  153 

travel  a  different  road  from  the  others.  The  sugars  and 
proteids  pass  into  the  blood  capillaries  of  tJie  villi  (Y'\g.  76). 
TJie  fat  enters  tJie  lympJi  capillaries,  and  is  carried  to  the 
thoracic  duct,  which  empties  it  into  the  blood. 

The  Lymph  Nodes.  Scattered  through  the  body  are  many1 
white  bodies,  called  lymph  nodes.  The  largest  of  them  are 
perhaps  as  large  as  an  ordinary 
sized  marble,  though  somewhat 
flattened.  If  you  should  examine 
a  lymph  node,  you  would  find  that 


it  has  a  connective-tissue  coat  and  that 
it  is  filled  with  white  corpuscles.  The 
lymphatic  vessels  pour  the  lymph  into 
these  nodes,  where  it  filters  through  FlG>  y8>  The  ]ymphatic 

among  the  Corpuscles  in  the  node  much    vessels  and  nodes  of  a  part  of 

as  water  filters    through    sand   grains. 

After  passing  through  the  node,  the  lymph  is  taken  up 
and  carried  on  by  other  lymphatic  vessels.  The  lymph 
from  many  parts  of  the  body  passes  through  several  nodes 
before  it  reaches  the  blood. 

The  Function  of  the  Lymph  Nodes.  The  lymph  nodes  have 
two  functions  :  they  furnish  breeding  places  for  tJie  zvhite  cor- 
puscles, and  they  filter  out  disease  germs  that  get  in  among  the 
cells  and  are  taken  up  by  the  lymphatic  capillaries. 

1  There  are  six  or  seven  hundred  lymphatic  glands  in  the  body  large  enough  to 
be  seen  without  a  microscope  (Fig.  66). 


154  HUMAN  PHYSIOLOGY 

The  white  corpuscles  that  escape  from  the  blood  enter  the 
lymphatic  capillaries  and  are  carried  to  the  lymph  nodes. 
Inside  the  nodes  they  divide  and  form  new  corpuscles.  The 
corpuscles  reach  the  blood  again  by  passing  into  the  vessels 
that  flow  from  the  nodes  and  floating  in  the  lymph  to  the 
blood. 

Many  diseases  are  caused  by  germs  that  live  and  grow 
among  the  cells.  Some  of  these  germs  are  taken  up  by  the 
lymph  capillaries  and  carried  into  the  lymph  nodes.  The 
nodes  stop  the  germs,  and  the  corpuscles  in  the  nodes  kill 
them.  Thus  the  germs  are  kept  from  getting  into  the 
blood  and  being  carried  all  through  the  body.1 

HYGIENE 

The  heart  is  a  muscle,  and  it  is  by  far  the  hardest  worked 
of  all  the  muscles  of  the  body.  It  is  especially  hard-worked 
at  that  period  in  life  when  growth  is  very  rapid,  —  when  a 
boy  or  girl,  in  a  single  year,  becomes  almost  as  large  as  a 
man  or  a  woman.  Any  extra  strain  put  upon  the  heart  at 
this  time  is  very  likely  to  cause  trouble.  The  heart  also  be- 
comes weak  in  old  age,  and  old  persons  should  take  care  not 
to  overwork  their  hearts.  The  following  are  the  chief  causes 
of  injury  to  the  heart : 

Severe  Exercise.  Exercise  of  the  muscles  greatly  increases 
the  work  of  the  heart.  Hard  work  causes  any  muscle  to  en- 
large, and  the  extra  work  thrown  on  the  heart  by  severe 
exercise  may  cause  "  athletic  heart."  In  this  condition  the 

1  In  cancer,  "  cancer  cells  "  are  carried  into  the  lymph  nodes  that  receive  the 
lymph  from  the  diseased  tissue,  and  set  up  their  growth  there.  It  is  impossible 
to  treat  the  disease  successfully  after  the  cancer  cells  have  reached  the  lymph 
nodes  that  lie  deep  in  the  body.  It  is  important,  therefore,  that  a  physician  be 
consulted  at  the  earliest  possible  moment. 


THE   CIRCULA TOR  Y  SYSTEM  I  5  5 

heart  is  enlarged,  sometimes  to  several  times  its  natural  size. 
This  enlarging  of  the  heart  is  frequently  followed  by  a  re- 
laxation of  the  heart  and  of  the  arterial  walls.  The  openings 
where  the  valves  are  placed  are  enlarged  until  the  valves 
do  not  completely  close  them.  The  valves  then  leak  and  part 
of  the  blood  flows  backward  in  the  circulation.  This  blood 
must  be  pumped  twice,  so  the  work  of  the  heart  is  in- 
creased. Very  hard  work  may  also  cause  fatty  degeneration 
of  the  heart. 

Boys  often  injure  their  hearts  by  bicycle  riding.  Football 
sometimes  injures  the  heart,  requiring  too  long-continued  and 
too  severe  exercise  for  any  but  those  with  naturally  strong 
hearts.  Too  much  playing  of  tennis  may  also  overtax  the 
heart,  and  any  other  severe  and  long-continued  exercise  may 
do  the  same.  It  is  well  to  keep  in  mind  that  the  time  of 
life  when  the  heart  is  most  frequently  injured  is  in  youth. 

Headache  Remedies.  A  great  number  of  headache  reme- 
dies are  manufactured  from  coal  tar.  They  are  powerful 
depressors  of  the  heart,  and  many  people  have  injured  their 
hearts  with  them.  They  are  useful  medicines,  but  very  dan- 
gerous to  take  except  under  the  advice  of  a  physician. 

Alcohol.  The  effects  of  alcohol  on  the  heart  and  blood 
vessels  are  very  serious.  It  sometimes  causes  a  paralysis  of 
the  muscles  in  the  small  vessels,  so  that  they  are  always  dis- 
tended with  blood,  as  you  may  have  seen  in  the  face  and 
eyes  of  one  who  uses  alcohol  excessively.  It  weakens  the 
arteries  by  causing  a  fatty  degeneration  and  a  hardening 
of  the  arterial  walls.  Apoplexy  (the  bursting  of  a  blood 
vessel  in  the  brain)  is  therefore  more  frequent  among  alco- 
holics than  among  abstainers  from  alcohol.  Alcohol  also 
sometimes  causes  great  quantities  of  fat  to  be  deposited  upon 
the  heart,  thus  interfering  with  its  work ;  it  so  affects  the 


156  HUMAN  PHYSIOLOGY 

nervous  control  of  the  heart  that  the  action  of  the  whole 
organ  is  weakened. 

The  use  of  alcohol  also  overworks  the  heart.  It  takes 
more  force  to  pump  the  blood  out  of  the  heart  into  hard,  stiff- 
walled  vessels  than  is  required  to  pump  it  into  vessels  with 
elastic  walls.  The  work  of  the  heart  is  therefore  increased 
when  the  arterial  walls  are  hardened  by  the  use  of  alcohol. 
This,  like  hard  exercise,  overworks  the  heart,  and  brings  on 
enlargement  of  the  heart,  trouble  with  the  valves,  and  fatty 
degeneration.  Beer  drinkers  in  particular  suffer  from  heart 
disease,  because  in  addition  to  enduring  all  the  evil 
effects  of  alcohol,  a  beer  drinker's  heart  is  required  to 
pump  through  the  system  the  great  quantities  of  water 
taken  in  the  beer. 

Of  course,  from  reading  the  above  you  are  not  to  understand 
that  every  one  who  takes  alcohol  into  his  body  must  have  all 
these  diseases  of  the  heart.  You  are  to  understand,  however, 
that  the  effects  of  alcohol  on  the  heart  are  bad,  and  that  heart 
disease  is  much  more  common  among  those  who  use  alcohol 
than  among  those  who  abstain  from  alcohol.  With  such  an 
important  organ  as  the  heart,  no  one  can  afford  to  take  the 
chance  of  weakening  it  in  any  way,  for  even  though  in  health 
it  may  seem  to  be  doing  its  work  without  difficulty,  in  an 
attack  of  pneumonia  or  other  severe  illness,  when  everything 
depends  on  the  heart's  holding  out  for  a  few  days  longer,  jt 
may  suddenly  fail.  Statistics  from  a  Munich  hospital  show 
that  1 6  per  cent  of  all  deaths  in  the  hospital  were  due  to 
"beer  drinker's  heart,"  the  weakened  hearts  failing  under  the 
strain  of  disease. 

Tobacco.  Tobacco  so  affects  the  heart  nerves  that  the 
action  of  the  heart  becomes  unsteady, —  sometimes  beating 
very  hard  and  fast,  and  sometimes  with  a  weak,  fluttering 


THE   CIRCULATORY  SYSTEM  157 

beat.  This  trouble  is  known  as  "  tobacco  heart,"  and  is  very 
common  among  young  cigarette  smokers. 

Summary.  The  body  cannot  live  without  the  circulation 
of  the  blood,  because  it  is  the  blood  that  carries  the  food, 
oxygen,  and  water  to  the  cells,  takes  away  the  wastes  from 
the  cells,  and  distributes  the  body  heat. 

The  blood  is  pumped  through  the  body  by  the  heart.  It 
leaves  the  heart  through  the  arteries,  passes  through  the 
capillaries,  and  comes  back  to  the  heart  through  the  veins. 
As  it  passes  through  the  capillaries  it  gives  food  and  oxygen 
to  the  cells  and  takes  up  the  cell  wastes. 

The  blood  is  composed  of  corpuscles  and  plasma.  The 
plasma  escapes  through  the  capillary  walls  and  passes  out 
among  the  cells.  It  is  then  called  lymph.  The  lymph  is 
taken  up  by  the  lymphatic  vessels  and  returned  to  the 
blood. 

The  heart  is  sometimes  injured  by  too  severe  exercise, 
headache  remedies,  alcohol,  and  tobacco. 


QUESTIONS 

Give  three  great  laws  according  to  which  the  body  lives.  MVhat  is 
the  function  of  the  blood?  ^Explain  why  the  circulation  of  the  blood 
is  necessary. 

^What  are  the  circulatory  organs?  Locate  and  describe  the  heart. 
Of  what  are  the  walls  of  the  heart  composed?  How  many  cavities 
are  in  the  heart,  and  what  are  they  called  ?  Why  are  the  walls  of 
the  ventricles  thicker  than  the  walls  of  the  auricles?  What  is  the 
function  of  the  heart? 

Describe  a  contraction  of  the  heart.  What  is  the  average  rate  of 
the  heart  beat  ?  How  fast  does  your  own  heart  beat? 

Where    are    the   valves   in   the  heart?      What  is  their  function? 


158  HUMAN  PHYSIOLOGY 

Describe  the  way  the  valves  in  the  heart  close  the  openings  between 
the  auricles  and  the  ventricles;  the  way  they  close  the  openings 
from  the  arteries  into  the  heart. 

^What  is  an  artery?  a  vein?  a  capillary?  How  does  the  blood 
flow  in  each  of  these  vessels  ?  ^How  does  it  get  from  the  arteries 
into  the  veins  ? 

How  do  the  walls  of  arteries,  veins,  and  capillaries  differ  ?  How 
is  the  size  of  the  opening  in  an  artery  changed  ?  What  advantage 
is  this  to  the  body? 

Trace  the  course  of  the  blood  from  right  auricle  to  right  auricle. 
How  long  does  it  take  the  blood  to  make  this  circuit? 

What  two  kinds  of  nerves  are  connected  with  the  heart?  with 
the  arteries?  What  proof  can  you  give  that  the  blood  vessels  are 
controlled  by  the  nervous  system  ? 

How  much  of  the  body  weight  is  blood?  Of  what  is  blood  com- 
posed? What  is  the  liquid  part  of  the  blood  called?  What  two 
kinds  of  corpuscles  are  in  the  blood?  How  abundant  are  the  red 
corpuscles?  the  white? 

V/What  is  the  function  of  the  plasma?  Where  are  the  white  cor- 
puscles formed  (page  153)?  Explain  how  they  escape  from  the 
capillaries.  NAVhat  is  the  function  of  the  white  corpuscles? 

What  shape  has  a  red  corpuscle  ?  Where  are  the  red  corpuscles 
formed?  What  becomes  of  them ?\»  What  is  their  function?  What 
substance  in  them  carries  the  oxygen?  Explain  how  it  does  this. 
How  is  carbon  dioxid  carried  in  the  blood  ?  Why  is  carbon  dioxid 
injurious  to  the  cells  ? 

^ Where  in  the  body  is  the  blood  red?  N Where  is  it  dark?     What 
Xis  lymph?   >JVhat  is  the  function  of  lymph?     How  does  the  life  of 
one  of  the  body  cells  resemble  the  life  of  a  small  animal  in  a  pond  of 
water  ? 

What  is  the  function  of  the  lymphatic  vessels?  Where  do  the 
vessels  from  the  upper  part  of  the  right  side  of  the  body  empty  into 
the  blood  ?  What  vessel  drains  the  lymph  from  the  remainder  of  the 
body?  Where  does  this  vessel  empty  into  the  blood?  How  do 


THE   CIRCULATORY  SYSTEM  159 

the  absorbed  sugar  and  proteids  reach  the  blood?  How  do  the 
absorbed  fats  reach  the  blood? 

Describe  a  lymph  node.  How  is  the  lymph  carried  into  and 
through  it?  What  two  functions  have  the  lymph  nodes? 

At  what  times  of  life  is  the  heart  especially  likely  to  be  injured  ? 
Why  does  too  severe  exercise  hurt  the  heart?  In  enlargement  of 
the  heart,  what  trouble  is  -there  with  the  valves  ?  What  effect  has 
this  on  the  amount  of  work  the  heart  must  do?  Name  some  of  the 
forms  of  exercise  that  are  likely  to  injure  the  heart. 

What  effect  have  headache  remedies  on  the  heart?  What  effect 
has  alcohol  on  the  small  vessels?  on  the  walls  of  the  arteries? 
What  does  this  sometimes  cause  ?  WThat  does  alcohol  cause  to  be 
deposited  about  the  heart?  How  does  alcohol  increase  the  work  of 
the  heart?  What  additional  work  does  a  beer  drinker's  heart  have? 
Why  is  it  unsafe  to  risk  injuring  the  heart?  What  per  cent  of  deaths 
in  a  Munich  hospital  were  due  to  beer  drinker's  heart?  What  is  the 
effect  of  tobacco  on  the  heart? 


Press  on  a  vein  in  your  wrist  with  one  finger.  On  the  side  of  the 
finger  toward  the  heart  empty  the  vein  by  rubbing  another  finger 
along  it.  Does  the  blood  flow  back  into  the  vein  ?  On  the  other  side 
of  the  finger  that  is  pressing  the  vein,  rub  the  blood  away  from  the 
heart.  Does  the  blood  flow  back  into  the  vein  ?  Explain. 

Explain  why  a  steady  stream  of  water  comes  out  of  the  end  of  a 
long  rubber  hose  into  which  water  is  being  pumped  with  intermittent 
strokes.  The  blood  in  the  arteries  flows  in  spurts,  and  in  the  capilla- 
ries and  veins  it  flows  in  a  steady  stream.  Explain  why  it  does  this. 
Why  does  it  require  more  force  to  pump  water  into  an  iron  pipe  than 
into  a  rubber  hose  with  elastic  walls  ? 

Does  a  wave  on  a  river  travel  with  the  same  speed  as  the  water  in 
the  river?  Do  the  blood  and  the  wave  in  the  blood  that  causes  the 
pulse  in  an  artery,  travel  with  the  same  speed  ? 


CHAPTER   XII 


RESPIRATION 

WATCH  the  chest  of  some  one  who  is  near  you,  and  you 
will  see  that  it  alternately  rises  and  falls.  As  the  chest 
rises,  air  is  taken  into  the  lungs.  This  is  called  inspiration. 
When  the  chest  falls,  the  air  is  driven  out  of  the  lungs. 
This  is  expiration.  The  whole  process  of  taking  the  air  into 
the  lungs  and  sending  it  out  of  them  is  called  breathing,  or 
respiration.  Like  the  circulation  of  the  blood,  respiration 
goes  on  night  and  day  as  long  as  the  body  lives. 

The  Object  of  Respiration.  The  object  of  respiration  is  to 
take  oxygen  into  tJie  body  and  to  give  off  carbon  dioxid  front  the 
body.  When  the  blood  passes  through 
the  lungs,  it  takes  up  a  new  oxygen  sup- 
ply for  the  cells,  and  loses  the  carbon 
dioxid  which  it  has  carried  away  from  the 
cells.  Without  respiration,  the  circulation 
of  the  blood  would  be  useless,  for  the 
blood  could  not  obtain  oxygen,  and  it 
would  carry  through  the  body  again  and 
again  the  poisonous  carbon  dioxid  which 
it  takes  up  from  the  cellfc 

Why  Oxygen  is  Necessary  to  the  Cells. 
When  the  foods  are  oxidized  (burned) 
within  the  cells,  the  atoms  of  the  foods  unite  with  atoms  o'f 
oxygen.  By  this  process,  energy  is  given  to  the  cells  (page 

160 


FIG.  79.    Burning  low  for 
lack  of  oxygen. 


RESPIRATION  l6l 

114).  If  there  are  no  oxygen  atoms  in  the  cells  for  the  food 
atoms  to  unite  with,  it  is  evident  that  the  oxidation  of  the 
foods  within  the  cells  must  come  to  a  stop.  The  cells  will 
then  be  unable  to  get  energy,  and  they  will  die.  Without 
oxygen  they  cannot  use  the  food,  and  without  oxygen  they 
starve  to  death  for  lack  of  energy  as  surely  as  if  no  food  had 
reached  the  cells.  Oxygen  is  necessary  tJiat  the  foods  may  be 
burned  within  the  cells.  As  oxygen  is  necessary  for  the  burn- 
ing of  the  foods  within  the  cells,  so  it  is  necessary  for  the 
burning  of  all  substances  everywhere.  Cover  a  candle  by  set- 
ting a  glass  vessel  over  it  (Fig.  79).  In  a  few  moments  the 
candle  will  go  out  because  there  is  no  more  oxygen  in  the 
vessel. 

THE  ORGANS   OF   RESPIRATION 

The  organs  of  respiration  include  the  framework  of  the 
chest,  the  muscles  that  are  used  in  breatJiing,  the  lungs,  and 
the  air  passages.  The  lungs  are  the  most  prominent  of  these 
organs,  and  it  is  in  them  that  the  blood  gives  off  its  carbon 
dioxid  and  takes  up  its  oxygen.  Most  of  the  diseases  of  the 
respiratory  organs  are  caused  by  germs  that  grow  on  the 
warm,  moist  lining  of  the  air  passages,  and  in  the  air  sacs  of 
the  lungs. 

The  Lungs.  The  lungs  (Fig.  84)  are  composed  chiefly  of 
a  great  mass  of  air  passages  and  air  sacs.  They  therefore 
have  a  light  and  spongy  structure.  In  the  lungs  blood  ves- 
sels are  very  abundant,  for  at  each  beat  of  the  heart  as  much 
blood  goes  to  them  as  goes  to  all  the  remainder  of  the  body. 
The  lungs  are  hung  in  the  thoracic  cavity  by  the  trachea 
(Fig.  82),  through  which  air  passes  into  and  out  of  them. 
Each  lung  is  surrounded  with  a  thin  connective  tissue  sac 
called  SL  pleura  (plural,  pleura). 


1 62 


HUMAN  PHYSIOLOGY 


The  Thoracic  Cavity. 


FIG.  80.     The  divisions  of  the 
thoracic  cavity. 


The  thoracic  cavity  (Fig.  8)  lies 
within  the  framework  of  the  chest, 
and  the  diaphragm 1  forms  its  floor. 
It  is  divided  longitudinally  into  three 
chambers  (Fig.  80).  In  each  side 
chamber  lies  a  lung.  In  the  central 
chamber  the  heart  and  the  bases  of 
the  great  blood  vessels,  the  trachea, 
and  the  esophagus  are  found.  The 
central  chamber  is  wider  in  its  lower 
front  portion  where  the  heart  lies,  and 
>  narrower  above  and  behind  the  heart. 
The  pleura  are  two 

I 


ARTERY 
\ 


The  Pleurae. 

thin,  double-walled  sacs.  The  outer 
layer  of  a  pleura  is  attached  to 
the  chest  wall  and  diaphragm,  and 
stretches  as  a  partition  across  the 
thoracic  cavity  from  top  to  bottom. 
The  inner  layer  incloses  the  lung. 
This  layer  of  the  pleura  is  very 
delicate,  and  forms  a  thin  coat  over  , 

FIG.  81.     Air  sacs  and  blood 

the  surface  of  the  lung.     In  Figure  vessels  in  the  lungs.   The  blood 

8O     yOU       Can       See       how      the      Chest    capillaries  lie  in  the  thin  walls 
,..,,.    A  . 

cavity   is   divided    into    three 


parts 


of  the  air  sacs.    As  the  blood 

passes  through  the  capillaries 

by     the     pleurae,    and      in      Figure      82    carbon   dioxid   and  water  pass 

you    can     trace     a    pleura    entirely  out  into  th,e  air  sac'  and  oxuy- 

J  J     gen  passes  from  the  sac  into  the 

around    a     lung     and     around     the  blood. 


1  The  diaphragm  (Fig.  8)  is  a  thin  sheet  of  muscle  with  a  connective  tissue 
center.  It  is  dome-shaped,  the  stomach  and  liver  fitting  into  the  hollow  in  its 
lower  surface.  Viewed  from  above,  the  diaphragm  appears  as  a  ring  of  muscle 
with  a  connective  tissue  center.  It  is  attached  all  around  by  its  outer  edge  to  the 
body  wall,  specially  heavy  bands  of  muscles  running  down  and  attaching  them- 


RESPIRATION' 


163 


cavity  in  which  the  lung  lies.1  The  surfaces  of  the  pleurae 
are  kept  moist  with  a  thin  yellowish  liquid.2  This  prevents 
friction  when  the  two  layers  of  the  pleura  move  on  each 
other  in  breathing. 


FIG.  82.     The  pleurae. 


How  the  Chest  is  enlarged  in  Inspiration.  In  inspiration 
the  chest  is  enlarged  in  two  ways.  The  ribs  and  stermim  are 
lifted  up  and  out,  widening  the  cavity  of  the  chest.  The  dia- 
phragm is  drawn  downward,  causing  the  bottom  of  the  chest 
cavity  to  sink,  and  thus  increasing  the  size  of  the  cavity.  The 

selves  to  the  front  of  the  spinal  column.     When  the  muscles  of  the  diaphragm 
contract  and  shorten,  they  draw  its  top  (center)  downward. 

1  The  pupil  should  also  trace  out  the  course  of  the  pericardium  and  note 
that  it  is  a  double-walled  sac  enveloping  the  heart  as  a  pleura  envelops  a  lung. 

2  The  disease  called  pleurisy  is  inflammation  of  the  pleurae.     In  this  disease 
considerable  quantities  of  liquid  may  collect  between  the  two  layers  of  the  pleurae. 


164  HUMAN  PHYSIOLOGY 

chest  walls  and  the  diaphragm  are  thus  drawn  away  from  the 
lungs,  leaving  a  vacuum,  or  empty  space,  between  the  two 
layers  of  the  pleurae.  The  air  then  rushes  down  into  the  lungs, 
and  expands  them  until  they  fill  the  enlarged  thoracic  cavity. 
So  promptly  do  the  lungs  expand  and  follow  up  the  chest 
walls  and  diaphragm  in  inspiration  that  there  is  no  noticeable 
space  between  the  two  layers  of  the  pleurae. 

Expiration.  In  ordinary  expiration,  the  muscles  do  little 
work.  The  ribs  and  sternum  sink  chiefly  from  their  own 
weight,  and  the  diaphragm  is  pushed  1  up  by  the  liver,  stomach, 
and  other  abdominal  organs  below  it.  This  with  the  elasticity 
of  the  lungs  drives  out  the  air;  for  just  as  the  stretched  walls 
of  a  blown-up  football  or  of  a  toy  balloon  expel  the  air,  so  the 
stretched  walls  of  the  air  sacs  and  of  the  small  bronchial  tubes 
help  to  force  the  air  out  of  the  lungs. 

The  Nasal  Passages  and  the  Pharynx.  When  air  is  taken 
into  the  lungs,  it  first  enters  the  nasal  passages  (Fig.  83). 
These  are  two  narrpw  chambers  that  run  up  in  the  head  as 
high  as  the  eyes  and  backward  about  four  inches.  An  open- 
ing in  the  floor  of  each  nasal  chamber  at  the  back  leads  down 
into  the  pharynx. 

The  pharynx  is  a  funnel-shaped  cavity  lying  behind  the 
mouth.  It  curves  around  the  base  of  the  tongue,  with  its 
mouth  opening  forward.  Hanging  down  in  front  of  the 
openings  from  the  nasal  chambers  and  helping  to  separate  the 
mouth  from  the  pharynx  is  a  little  curtain-like  structure  called 

1  When  the  diaphragm  comes  down  in  inspiration,  it  forces  the  organs  below  it 
downward  and  pushes  the  abdominal  walls  outward.  In  expiration  the  stretched 
abdominal  walls  come  inward  partly  because  of  their  elasticity,  and  partly  because 
of  the  contraction  of  the  abdominal  muscles,  and  drive  the  diaphragm  upward. 
In  a  forced  expiration,  the  abdominal  muscles  contract  forcibly,  pulling  in  the  ab- 
dominal walls  and  driving  the  diaphragm  far  upward.  At  the  same  time  they 
draw  down  the  ribs  and  sternum,  to  which  they  are  attached  at  their  upper  ends. 


RESPIRATION  165 

the  uvula,  or  soft  palate.  In  swallowing,  the  uvula  is  pushed 
back  over  the  openings  from  the  nose  so  that  it  covers  them 
and  prevents  food  and  water  from  entering  the  nose  (Fig.  83). 

In  the  side  walls  of  the  pharynx,  directly  under  the  corners 
of  the  lower  jawbone,  the  two  tonsils 1  are  located.  When 
viewed  from  the  inside  of  the  pharynx,  the  tonsils  appear 
like  gentle,  rounding  elevations  lying  under  the  mucous  mem- 
brane which  lines  the  pharynx  walls.  At  the  bottom  of  the 
pharynx  are  two  openings,  one  leading  into  the  esophagus 
and  one  into  the  larynx. 

The  Larynx.  The  larynx  is  the  enlarged  upper  part  of 
the  trachea.  It  has  a  framework  of  cartilages,  which  you 
can  easily  feel  in  the  front  of  your  neck.  In  swallowing,  the 
food  and  drink  would  fall  down  into  the  larynx  if  it  were  not 
for  the  epiglottis  (Fig.  83).  This  flap-like  structure  stands 
in  front  of  and  above  the  opening  to  the  larynx,  and  in  swal- 
lowing the  larynx  is  drawn  up  and  forward,2  so  that  its  mouth 
is  pushed  up  in  under  the  epiglottis.  The  food  or  water 
then  passes  over  the  larynx  into  the  esophagus.  During 
breathing  the  larynx  drops  down,  leaving  its  mouth  open,  and 
allowing  the  air  to  pass  into  and  out  of  the  lungs.  The  vocal 
cords,  which  produce  the  sound  of  the  voice,  are  in  the  larynx. 

The  Trachea  and  its  Branches.  The  trachea  divides  into 
two  great  branches,  one  of  which  goes  to  each  lung.  Within 
the  lung  these  branches  divide  again  and  again,  until  finally 
they  end  in  little  air  sacs.  The  branches  of  the  trachea  are 

1  When  germs  get  into  the  tonsils  and  cause  inflammation,  the  disease  is  called 
tonsilitis. 

2  Feel  your  larynx  while  you  swallow,  and  note  how  it  rises.     If  one  laughs 
when  eating  or  drinking,  the  larynx  is  lowered  and  food  or  water  may  fall  down 
into  the  trachea.     When  food  or  liquid  is  driven  upward  through  the  pharynx  in 
laughing  or  by  vomiting,  it  may  pass  in  behind  the  uvula  and  enter  the  nasal  pas- 
sages from  the  rear. 


1 66 


HUMAN  PHYSIOLOGY 


called  the  bronchial  tubes.  In  the  walls  of  the  trachea  and 
of  all  the  larger  bronchial  tubes  are  rings  of  cartilage  to  keep 

the  air  passages  from 
closing  and  shutting 
off  the  supply  of  air  * 
from  the  air  sacs  in 
the  lungs. 

The  Air  Sacs.  Each 
small  bronchial  tube 
at  the  end  widens  out 
and  becomes  a  thin- 
walled  sac.  The  walls 
of  this  sac  are  thrown 
into  little  sac-like 
folds,  so  that  the  end 
of  a  bronchial  tube  is 
a  larger  sac  2  made  up 
of  a  great  number  of 

FIG. '83.     The  air  follows  the  path  indicated  by     little  SaCS,  all  Opening 
the  blue  arrows,  and  the  food  follows  the  path  indi-     •  i       ,  j       ,1 

center.    So  abundant 

are  the  air  sacs  in  the  lungs  that  their  estimated  number  is 
725,000,000,  and  if  they  were  all  opened  and  spread  out  side 
by  side,  they  would  cover  2150  square  feet  of  space. 

Changes  in  the  Air  in  the  Air  Sacs.     The  walls  of  the  air 
sacs    are    exceedingly    thin.      They    contain    a    very    great 

1  In  asthma  the  muscles  in  the  walls  of  the  small  bronchial  tubes  contract  so 
that  the  greatest  difficulty  is  experienced  in  getting  the  air  to  pass  in  and  out  of 
the  air  sacs.     In  pneumonia  the  small  air  passages  and  the  air  sacs  are  stopped 
up  with  mucus. 

2  The  larger  air  sacs  at  the  ends  of  the  bronchial  tubes  are  called  infundibula 
(singular,   infundibuhini}.     The   smaller  air  sacs  of  which  an  infunclibulum  is 
composed  are  called  alveoli  (singular,  alveolus). 


WHM  »  topf ' 

Of 


RESPIRATION 


I67 


number  of  delicate  blood  capillaries  through  which  all  the 
blood  in  the  body  passes  every  minute  and  a  quarter  (page 
145).  As  the  blood  flows  through  the  capillaries  in  the  walls 
of  the  air  sacs,  oxygen  from  the  air  passes  in  through  the 
walls  of  the  sacs  and  enters  the  blood,  and  carbon  dioxid 


FIG.  84.  The  trachea  and  the  lungs.  B  and  Cshow  the  way  the  small  bronchial 
tubes  end  in  air  sacs  (infundibula)  which  are  made  up  of  a  large  number  of  smaller  sacs. 

passes  out  from  the  blood  into  the  air  (Fig.  81).  Water  also 
passes  out  of  the  blood  into  the  air,  as  you  can  prove  by 
breathing  on  a  cold  window  pane,  and  the  air  is  warmed 
while  in  the  lungs.  The  air  in  the  lungs,  therefore,  loses 
oxygen,  and  gains  carbon  dioxid,  water,  and  heat. 

Perhaps  what  is  going  on  in  the  lungs  would  be  made  more  vivid 
to  you,  if,  in  imagination,  you  could  make  a  trip  down  into  the  lungs 
and  see  what  is  happening  there.  Following  down  the  trachea  and 
the  bronchial  tubes,  you  would  come  into  one  of  the  larger  air  sacs. 


168  HUMAN  PHYSIOLOGY 

There  you  would  see  all  about  you  the  mouths  of  the  little  air  sacs 
opening  into  the  chamber  in  which  you  were  standing.  Going  up  to 
the  mouth  of  a  small  sac  and  looking  in,  you  would  see  the  blood 
shooting  along  in  the  capillaries  in  the  walls.  As  the  blood  enters 
the  capillaries,  it  is  dark  in  color,  but  as  it  moves  along  it  gradually 
takes  on  a  redder  and  redder  hue  until  it  is  a  bright  scarlet  when  it 
gets  through  the  capillaries  and  starts  to  the  heart. 

Peering  still  more  closely  into  the  sac,  you  would  see  a  great  mul- 
titude of  little  oxygen  molecules  flying  from  the  air  into  the  blood, 
where  they  unite  with  the  hemoglobin  of  the  red  corpuscles  and  are 
carried  away.  You  would  also  see  the  carbon  dioxid  and  water 
molecules  flying  out  from  the  blood  into  the  air  in  the  little  sac,  and 
then  passing  out  into  the  larger  sac  and  up  into  the  bronchial  tubes, 
to  pass  out  of  the  lungs  in  the  breath. 

Mucus  and  Cilia.  The  entire  respiratory  tract  is  lined  with 
mucous  membrane  and  is  kept  moist  with  sticky  mucus. 
In  all  parts  of  it  except  in  the  pharynx  and  air  sacs  and  over 
the  vocal  cords,  the  walls  are  covered  with  cilia  (Fig.  6). 

The  mucus  on  the  walls  of  the  air  passages  catches  dust 
and  germs  that  are  in  the  air,  and  the  cilia  sweep  the  mucus 
and  matter  which  is  caught  in  the  mucus  out  of  the  air  pas- 
sages. The  air  is  thus  cleansed,  and  irritating  dust  particles 
and  dangerous  disease  germs  are  in  a  great  measure  prevented 
from  getting  down  into  the  delicate  air  sacs  of  the  lungs. 

The  nasal  passages  are  especially  fitted  for  purifying  and 
warming  the  inhaled  air.  The  nostrils  are  guarded  by  hairs 
for  straining  out  dust,  the  mucus  on  the  walls  of  the  long  and 
narrow  nasal  passages  catches  much  dust  and  many  germs, 
and  air  inhaled  through  the  nose  is  warmed  before  it  reaches 
the  throat  and  lungs.  Any  trouble  in  the  nasal  passages  1 

1  Adenoid  growths  or  nasal  polyps  may  cause  such  swelling  in  the  nasal 
chambers  that  the  air  passages  through  the  nose  are  completely  closed.  Deaf- 
ness also  is  caused  by  these  growths,  and  the  teacher  should  carefully  watch  his 
pupils  for  any  symptoms  of  them  (pages  253  and  270). 


RESPIRA  TlOtf  1 69 

that  interferes  with  breathing  through  the  nose  should 
receive  medical  attention  at  once,  for  in  mouth  breathing, 
cold  and  dusty  air  is  taken  into  the  throat  and  lungs.  This 
brings  on  many  diseases  of  those  parts. 

RESPIRATION   IN   OTHER  ANIMALS 

An  insect  has  no  lungs,  but  it  takes  in  air  through  a  great 
number  of  little  tracheae,  or  air  tubes,  which  open  along  the 
sides  of  its  body.  A  fish  has  very  thin  gills  through  which 
the  blood  flows.  The  fish  takes  water  into  its  mouth  and 
sends  it  backward  over  the  gills  and  out  through  the  gill  slits 
on  the  sides  of  its  neck.  As  the  water  passes  over  the  gills, 
the  oxygen  from  the  water  passes  into  the  blood,  and  the 
carbon  dioxid  from  the  blood  is  given  off  into  the  water. 
A  fish  cannot  live  in  boiled  water,  because  when  water  is 
boiled,  the  air  is  driven  out.  It  cannot  live  in  the  air, 
because  when  taken  out  of  the  water,  its  gills  stick  together, 
and  the  oxygen  cannot  get  in  among  the  gills  to  pass  into 
the  blood. 

The  frog,  instead  of  making  a  vacuum  in  his  chest  and  thus 
causing  the  air  to  pass  into  the  lungs,  takes  air  into  the  mouth, 
and  by  drawing  in  the  skin  under  its  chin,  forces  the  air 
downward.  Watch  a  frog  breathing,  and  note  how  the  throat 
works  out  and  in.  When  under  water,  the  frog  breathes  by 
absorbing  oxygen  through  its  thin,  moist  skin.  It  may  inter- 
est you  to  know  that  a  frog  does  not  drink  water,  but  absorbs 
this  also  through  the  skin,  the  water  passing  into  the  blood 
which  flows  in  the  capillaries  of  the  skin. 

A  bird  has  no  diaphragm  and  the  lungs  run  far  back  in  the 
body.  In  many  birds  branches  from  the  lungs  go  out  even 
into  the  hollow  bones. 


I/O  HUMAN  PHYSIOLOGY 


HYGIENE 

Five  points  connected  with  the  hygiene  of  the  respiratory 
system  are  worthy  of  notice.  The  first  is  in  regard  to  the 
effects  of  tight  clothing  about  the  body.  This  interferes  with 
the  respiratory  movements,  and  is  a  great  evil,  for  it  leads  to 
shallow  breathing,  in  which  the  air  passes  into  and  out  of  the 
trachea  and  larger  bronchial  tubes  without  sending  much  oxy- 
gen into  the  air  sacs  or  taking  much  carbon  dioxid  out  of  them. 

The  second  point  is  in  regard  to  the  danger  of  breathing 
dust.  Large  numbers  of  people  die  every  year  from  consump- 
tion, pneumonia,  diphtheria,  and  grip,  and  many  more  suffer 
from  catarrh  and  other  diseases  of  the  respiratory  organs. 

Practically  all  of  these  diseases  are  caused  by  germs  that  are 
inhaled  in  the  air.  Many  people  have  the  idea  that  these 
germs  are  floating  around  singly  in  the  air,  but  this  is  a  mis- 
take. They  are  sticking  to  dust  particles,  small  pieces  of  lint 
from  cloth,  and  other  little  particles  of  matter  that  are  in  the  air. 
Every  effort  should  be  made,  therefore,  to  keep  from  breathing 
dust.  Streets  should  be  kept  sprinkled,  and  when  floors  are 
swept,  as  little  dust  as  possible  should  be  raised.  Dust  should 
be  wiped  from  walls  and  furniture  with  a  damp  cloth,  and  not 
stirred  up  into  the  air.  Everything  possible  should  be  done  to 
prevent  the  inhalation  of  dust,  for  most  respiratory  diseases 
are  germ  diseases,  and  the  germs  are  frequently  carried  into 
the  nose,  throat,  and  lungs  by  dust. 

The  third  point  which  we  wish  to  mention  is  the  value  of 
deep  breathing  exercises}*  It  is  an  excellent  plan  for  every 
one.  several  times  a  day,  to  stand  erect,  as  directed  on  page 
/I,  fill  his  lungs  to  their  utmost  capacity,  hold  the  air  for  a 

1  It  is  well  to  know  that  breathing  exercises  are  very  injurious  to  any  one  who 
is  suffering  from  consumption. 


RESPIRA  TION  1 7 1 

few  moments,  and  then  slowly  and  steadily  exhale  it.  This 
takes  the  oxygen  deep  into  the  lungs,  brings  out  the  carbon 
dioxid,  and  quickens  the  heart  beat,  thus  starting  the  blood 
more  swiftly  through  the  whole  body. 

Outdoors,  in  the  fresh  air,  is  the  best  place  to  take  these 
breathing  exercises,  and  you  can  practice  them  as  you  walk 
to  and  from  school.  But  a  better  time  to  practice  them  is 
when  you  have  become  tired  from  sitting  over  some  task  for 
a  considerable  time.  Then  you  will  find  that  it  will  rest  and 
refresh  you  to  go  to  a  window,  open  it,  and  take  several  deep 
breaths  of  fresh  air.  In  school,  when  every  one  has  been 
sitting  quietly  until  the  respiration  has  become  shallow  and 
the  heart  beat  slow,  it  is  very  beneficial  to  throw  the  win- 
dows wide  open  and  have  everybody  stand  up  and  take 
several  deep  breaths,  along  with  some  stretching  exercises 
to  relieve  the  cramped  muscles.  A  couple  of  minutes  spent 
in  this  way  takes  very  little  time,  and  sets  everybody  to  work 
again  with  renewed  vigor.  You  must  take  care,  however,  not 
to  practice  breathing  exercises  so  vigorously  that  you  make 
yourself  dizzy,  or  you  may  do  yourself  more  harm  than  good. 

The  fourth  point  to  which  we  would  call  your  attention  is  in 
regard  to  the  use  of  alcohol.  Users  of  alcohol  are  particularly 
liable  to  attacks  of  pneumonia,  catarch  of  the  pharynx,  larynx, 
and  bronchial  tubes,  and  to  other  respiratory  diseases.  The 
chief  reason  for  this  seems  to  be  that  alcohol  weakens  the  power 
of  the  body  to  kill  germs.  We  shall  take  up  this  whole  subject 
in  a  later  chapter,  but  you  should  know  now  that  when  pneu- 
monia or  grip  is  abroad,  and  every  one  is  trying  to  keep  himself 
in  the  best  possible  health  so  that  he  will  be  able  to  kill  any  germs 
that  get  into  his  body,  drinking  alcohol,  even  in  small  amounts, 
will  greatly  lessen  the  power  of  the  body  to  resist  germs. 

The  last  point  which  we  would  ask  you  to  note  in  connec- 


1/2 


HUMAN  PHYSIOLOGY 


tion  with  the  hygiene  of  the  respiratory  organs  is  the  effect  of 
cigarette  smoking  on  the  lungs  and  on  the  health  of  the  whole 
body.  Users  of  cigarettes  very  commonly  inhale  the  smoke. 
This  smoke  is  irritating  to  the  air  passages  and  has  a  very 
injurious  effect  on  the  lungs.  In  addition  to  the  poisonous 
substance  that  is  in  the  tobacco,  cigarette  smoke  contains  a  gas 
called  carbon  monoxid  (page  149,  footnote).  Both  the  poison 
of  the  tobacco  and  the  carbon  monoxid  pass  into  the  blood  in 
the  capillaries  of  the  lungs  and  injure  the  cells  of  the  body. 


THE  VOICE 


The  Cartilages  of  the  Larynx. 


FIG.  85.  The  cartilages  of  the  larynx. 
A  and  B  show  the  cartilages  as  seen  from  the 
front.  C  is  the  back  of  the  cartilages  in  their 
natural  position.  D  is  a  longitudinal  section 
of  the  larynx  showing  the  vocal  cord  stretched 
from  the  thyroid  cartilage  in  front  to  the  vocal 
process  of  the  arytenoid  cartilage  at  the  back. 


The  walls  of  the  larynx  are 
mainly  composed  of  two 
great  cartilages,  the  thyroid 
and  the  cricoid.  The  thyroid 
cartilage  is  the  "  Adam's  ap- 
ple" which  you  can  feel  in 
the  front  of  your  throat.  It  is 
somewhat  V-shaped,  with  the 
opening  behind.  Set  upon 
end  a  partially  opened  book, 
and  it  will  represent  fairly 
well  the  shape  of  the  thyroid 
cartilage. 

The  cricoid  cartilage  forms 
a  complete  ring,  but  it  is  much 
narrower  in  front  than  be- 
hind (Fig.  85  B).  In  front, 
the  cricoid  lies  in  the  larynx 
wall  below  the  thyroid  (Fig. 
85  D),  but  at  the  back  its 


RESPIRA  TION  1 73 

wide  part  stands  up  between  the  two  wings  of  the  Jhyroid 
and  forms  the  back  wall  of  the  larynx  (Fig.  85  C). 

On  top  of  the  cricoid,  at  the  back,  stand  up  the  two  little 
arytenoid  cartilages.  Each  one  is  loosely  hinged  at  its  base, 
so  that  to  a  certain  extent  it  can  slide  outward  toward  the  side 
wall  of  the  larynx  or  inward  toward  the  other  arytenoid.  It 
has  on  the  inner  side  of  the  base  a  small  projection  called 
the  vocal  process  (Fig.  85  B\  to  which  the  back  end  of  the 
vocal  cord  is  attached. 

The  Vocal  Cords.  The  vocal  cords  are  insignificant  little 
bands  of  connective  tissue  that  run  along  the  side  walls  of 


FIG.  86.  The  mouth  of  the  larynx  viewed  from  above.  A  shows  the  position  of 
the  vocal  cords  (c)  in  deep  breathing ;  B  is  their  position  in  ordinary  breathing ;  and  C 
shows  them  brought  together  for  speaking  or  singing,  a  is  the  epiglottis. 

the  larynx  from  the  front  to  the  back.  They  are  attached 
to  the  thyroid  cartilage  in  front  and  to  the  vocal  processes 
of  the  arytenoid  cartilages  at  the  back.  They  are  buried  in 
the  mucous  membrane  that  lines  the  larynx,  and  are  therefore 
attached  to  the  side  wall  of  the  larynx  by  one  edge.  If  you 
will  gather  up  and  draw  out  a  fold  of  skin  on  the  back  of  the 
hand,  you  will  have  something  that  in  a  way  represents  a 
vocal  cord. 

The  Vocal  Cords  in  Action.  In  ordinary  breathing  the  vocal 
cords  lie  close  to  the  walls  of  the  larynx  and  are  not  affected 
by  the  air  as  it  passes  out  of  and  into  the  lungs.  In  talking 
or  singing  the  cords  are  drawn  out  from  the  walls  and  stretched 


174 


HUMAN  PHYSIOLOGY 


across  the  opening  of  the  larynx,  until  there  is  only  a  narrow 
slit  between  the  cords.  The  air  passing  out  over  the  tightly 
stretched  cords  causes  them  to  vibrate  and  produce  the  sound 
of  the  voice.  To  make  a  gentle  sound,  a  slight  current  of 
air  is  passed  over  the  vocal  cords.  To  make  a  loud  sound  a 
heavy  current  of  air  is  sent  out. 

How  the  Vocal  Cords  are  thrown  into  and  out  of   Action. 
The  vocal  cords  are  thrown  into  and  out  of  action  by  mus- 


FlG.  87.  Diagram  illustrating  how  the  vocal  cords  are  brought  into  action.  When 
the  points  of  the  arytenoid  cartilages  (represented  by  the  gates  in  the  diagram)  to  which 
the  cords  are  attached  are  turned  forward,  tjie  cords  lie  close  to  the  wall.  When  the 
cartilages  swing  out,  as  in  D,  the  cords  are  drawn  out  from  the  walls,  as  in  C. 

cles  that  are  attached  to  the  arytenoid  cartilages.  When  a 
sound  is  to  be  produced,  the  arytenoid  cartilages  are  made 
to  slide  inward  toward  each  other  and  are  rotated  (Fig.  87  D\ 
so  that  they  draw  the  vocal  cords  out  from  the  walls  (Fig. 
87  C).  The  cords  are  thrown  out  of  action  by  sliding  the 
arytenoid  cartilages  outward  and  rotating  them  so  that  the 
vocal  processes  point  forward  (Fig.  87  B\  This  allows  the 
cords  to  lie  close  to  the  larynx  walls  (Fig.  87  A). 

The  Pitch  of  the  Voice.  The  heavy  strings  of  a  guitar  or 
of  a  violin  give  a  low  tone,  and  the  light  strings  give  a  high 
tone.  In  strings  of  the  same  weight,  a  tight  string  gives  a 


RESPIRATION*  175 

higher  tone  than  a  loose  string,  and  a  short  string  a  higher 
tone  than  a  long  string,  as  you  can  tell  by  tightening  the 
strings  on  a  stringed  instrument,  and  changing  their  lengths 
by  fingering  them.  The  pitch  of  the  sound  depends,  there- 
fore, on  the  weight,  the  length,  and  the  tightness  of  the  string. 

Persons  who  have  long  and  heavy  vocal  cords  have  low 
voices,  and  persons  with  short  and  light  vocal  cords  have 
high  voices.  The  larynx  of  a  man  is  larger  than  the  larynx 
of  a  woman,  his  vocal  cords  are  larger  and  longer,  and  his 
voice  has,  therefore,  a  lower  pitch.1 

Change  of  pitch  in  the  voice  is  brought  about  by  the  mus- 
cles of  the  larynx  tightening  and  loosening  the  vocal  cords. 
When  a  low  tone  is  to  be  produced,  the  cords  are  loosened. 
When  a  high  tone  is  to  be  produced,  the  cords  are  tight- 
ened. When  one  thinks  how  many  notes  a  singer  makes 
in  a  few  minutes,  tightening  the  vocal  cords  just  enough  to 
give  the  right  pitch  to  each  one,  he  realizes  how  rapidly  and 
accurately  the  muscles  of  the  larynx  must  work. 

Summary.  Respiration  is  necessary  to  take  in  oxygen  and 
g?ve  off  carbon  dioxid.  The  lungs  are  in  the  thoracic  cavity. 
Th's  cavity  is  enlarged  and  air  drawn  into  the  lungs  by 
lifting  up  the  framework  of  the  chest  and  by  pulling  down 
the  diaphragm. 

The  air  passes  through  the  nasal  passages  and  pharynx, 
enters  the  larynx,  and  goes  down  the  trachea  and  its 
branches  into  the  air  sacs  of  the  lungs.  In  the  air  sacs  it 
gives  up  its  oxygen  to  the  blood  and  takes  up  carbon  dioxid 
and  water  from  the  blood.  The  air  passages  are  lined  with 

1  When  male  and  female  voices  sing  in  unison,  the  male  voices  are  an  octave 
lower  than  the  female.  At  the  time  when  a  boy's  voice  changes,  the  larynx  sud- 
denly grows  very  much  larger,  and  the  vocal  cords  are  lengthened.  While  the 
voice  is  changing  it  should  not  be  given  any  severe  use. 


1/6  HITMAN-  PHYSIOLOGY 

mucous  membrane,  and  in  most  parts  the  walls  are  covered 
with  cilia.  The  mucus  catches  dust,  and  the  cilia  sweep  it 
out  of  the  air  passages. 

Tight  clothing  about  the  body  interferes  with  breathing ; 
many  diseases  of  the  respiratory  organs  come  from  breathing 
dust ;  deep  breathing  exercises  are  very  valuable  ;  alcohol 
brings  on  lung  diseases;  and  cigarette  smoking  injures  the  lungs. 
The  cartilages  of  the  larynx  are  the  thyroid,  cricoid,  and 
arytenoids.  The  vocal  cords  are  attached  to  the  thyroid  in 
front  and  to  the  arytenoids  behind.  In  speaking  or  singing, 
the  vocal  cords  are  thrown  out  from  the  wall,  and  the  voice 
is  produced  by  passing  a  current  of  air  over  the  cords.  The 
pitch  of  the  voice  depends  on  the  weight,  length,  and  tight- 
ness of  the  cord. 

QUESTIONS 

What  is  inspiration?  expiration?  respiration?  By  observing  the 
breathing  of  some  person  who  does  not  know  what  you  are  doing,  find 
out  how  many  times  he  breathes  in  a  minute. 

\>What  is  the  object  of  respiration?  Why  is  oxygen  necessary  to 
the  body?  Of  what  are  the  lungs  chiefly  composed?  How  much 
blood  goes  to  the  lungs?  What  is  the  covering  of  a  lung  called? 
Into  how  many  parts  is  the  thoracic  cavity  divided?  What  is  in  the 
side  chambers  of  the  thoracic  cavity?  the  middle  chamber?  Make  a 
drawing  showing  the  location  of  a  pleura. 

In  what  two  ways  is  the  chest  enlarged  ?  How  is  the  air  forced 
out  of  the  lungs?  Trace  the  air  down  into  the  lungs,  naming  the 
different  parts  of  the  air  passages.  Describe  the  nasal  passages. 
How  does  the  air  get  from  the  nasal  chambers  into  the  mouth? 

Describe  the  pharynx.  What  separates  the  pharynx  from  the 
mouth?  What  is  its  use?  Where  are  the  tonsils?  How  are  food 
and  water  kept  from  falling  into  the  larynx? 

Describe  the  branching  of  the  trachea.     What  are  the  branches  of 


RESPIRA  T/OAT  1 7  7 

the  trachea  called?  How  are  the  trachea  and  bronchial  tubes  kept 
open?  Describe  an  air  sac.  In  what  length  of  time  does  all  the 
blood  in  the  body  pass  through  the  lungs?  What  passes  from  the  air 
into  the  blood  ?  from  the  blood  into  the  air? 

With  what  is  the  respiratory  tract  lined?  How  is  it  kept  moist? 
What  parts  of  the  respiratory  tract  are  covered  with  cilia?  What  is 
the  use  of  the  mucus?  of  the  cilia?  What  are  the  nasal  passages 
especially  fitted  to  do?  Why  is  mouth  breathing  harmful? 

How  does  an  insect  breathe  ?  a  fish  ?  Why  cannot  a  fish  live  m 
boiled  water?  in  the  air?  How  does  the  frog  take  air  into  its  lungs? 
How  does  it  breathe  while  in  the  water?  How  does  a  frog  take 
water  into  its  body?  What  is  peculiar  about  a  bird's  lungs? 

Why  is  tight  clothing  harmful?  Name  five  diseases  caused  by 
breathing  in  germs  from  the  air.  How  are  germs  carried  in  the 
air?  What  measures  are  useful  in  keeping  down  dust? 

What  effect  have  deep  breathing  exercises  on  the  heart  beat  and 
circulation?  Where  should  such  exercises  be  taken?  when?  To 
what  respiratory  diseases  are  users  of  alcohol  particularly  liable? 

Name  the  two  large  cartilages  in  the  larynx.  Describe  the  thy- 
roid cartilage;  the  cricoid.  Where  are  the  arytenoid  cartilages? 
How  can  they  be  moved  ?  Describe  the  vocal  cords.  To  what  are 
they  attached  at  the  front?  at  the  back?  along  the  edge? 

What  is  the  position  of  the  vocal  cords  in  ordinary  breathing? 
in  talking  or  singing?  How  is  the  voice  produced?  How  is  a 
gentle  sound  produced?  a  loud  sound?  How  are  the  vocal  cords 
thrown  into  action?  out  of  action? 

Upon  what  does  the  pitch  of  a  sound  depend?  What  kind  of 
vocal  cords  have  persons  with  low  voices?  persons  with  high  voices? 
Why  has  a  man's  voice  a  lower  pitch  than  a  woman's  voice?  How 
is  the  pitch  of  the  voice  changed? 

When  a  bucket  is  lowered  in  water,  what  causes  the  water  to  rush 
into  it?  We  live  at  the  bottom  of  an  ocean  of  air.  What  causes 
the  air  to  be  drawn  into  the  lungs  when  the  chest  cavity  is  enlarged  ? 


CHAPTER   XIII 

VENTILATION 

OF  all  the  evils  that  befell  man  when  he  left  his  forest 
l\ome  and  came  to  dwell  within  walls  and  doors,  the  lack  of 
fresh  air  is  the  greatest.  By  its  own  activity,  the  body  is 
constantly  manufacturing  great  quantities  of  a  very  poisonous 
gas,  —  carbon  dioxid.  As  long  as  man  dwelt  in  the  great 
outdoors,  all  that  was  necessary  was  for  the  body  to  get  this 
gas  outside  of  itself,  and  the  ever  moving  currents  of  air 
carried  it  away  where  it  could  not  reenter  the  lungs.  But 
within  doors,  when  the  lungs  have  thrown  off  the  carbon 
dioxid,  they  often  find  their  work  of  no  avail,  for  the  air  is 
imprisoned,  and  the  carbon  dioxid  is  breathed  again  into  the 
lungs,  reenters  the  body,  and  poisons  the  cells.  The  cells 
then  become  weak  and  diseased,  and  fail  in  their  work. 
Disease  germs  creep  in,  the  weakened  body  cannot  kill  them, 
and  the  troubles  thus  started  often  end  only  with  the  end  of 
life.  So  we  say  again,  that  of  all  the  evils  that  have  come  to 
civilized  man  because  he  dwells  within  doors,  the  lack  of 
fresh  air  is  the  greatest. 

The  Air.  The  air  consists  of  about  four  fifths  nitrogen 
and  one  fifth  oxygen,  with  small  amounts  of  several  other 
gases  which  vary  at  different  times  and  places.  Among  the 
gases  that  exist  in  small  quantities  in  the  air  is  carbon  dioxid, 
which  in  ordinary  air  makes  up  nearly  4  parts  in  10,000. 
The  nitrogen  is  not  used  in  the  body,  but  passes  into  and  out 
of  the  lungs  unchanged.  It  is  the  oxygen  and  the  carbon 
dioxid  that  have  an  interest  for  us. 

178 


VENTILA  TION  1 79 

The  Supply  of  Oxygen.  Twenty-one  per  cent  of  the  air  is 
oxygen.  It  is  absolutely  necessary  for  life,  but  under  ordi- 
nary circumstances  the  air  and  the  blood  always  contain 
enough  oxygen  for  the  cells.  As  long  as  more  than  10  per 
cent  of  the  air  is  oxygen,  a  person  lives  as  well  as  if  he  were 
breathing  pure  oxygen.  Expired  air  still  contains  15  percent 
of  oxygen,  so  there  would  be  no  lack  of  oxygen  in  the  body, 
even  though  the  air  were  breathed  twice. 

Carbon  Dioxid.  Air  contains  a  little  less  than  4  parts  in 
10,000  of  carbon  dioxid.  Expired  air  contains  about  430 
parts  in  10,000  of  carbon  dioxid.  Stating  it  in  another  way, 
ordinary  air  is  .04  per  cent  carbon  dioxid,  and  expired  air  is 
4.3  per  cent  carbon  dioxid.  The  air  that  leaves  the  lungs, 
therefore,  contains  more  than  a  hundred  times  as  much  car- 
bon dioxid  as  the  air  that  enters  them.  It  is  the  carbon 
dioxid  in  the  air  which  is  so  injurious  in  crowded  and  poorly 
ventilated  buildings,  and  the  great  problem  of  ventilation  is 
how  to  get  rid  of  carbon  dioxid. 

Effects  of  Carbon  Dioxid  Poisoning.  A  small  amount  of 
carbon  dioxid  in  the  air  causes  drowsiness,  mental  dullness,  and 
a  slight  headache,  which  may  become  more  severe  if  the  carbon 
dioxid  is  breathed  for  a  long  time.  Long-continued  exposure 
to  carbon  dioxid,  as  when  one  works  or  lives  in  poorly  venti- 
lated quarters,  causes  paleness  and  general  weakness  and  ill 
health.  A  very  large  amount  of  carbon  dioxid  in  the  air 
causes  trembling  and  weakness,  followed  by  stupor  and  death 
if  the  breathing  of  the  gas  is  prolonged.  The  "choke  damp  " 
sometimes  found  in  coal  mines  is  carbon  dioxid,  and  carbon 
dioxid  is  sometimes  found  in  dangerous  quantities  in  old  wells.1 

1  Before  descending  into  a  well  it  is  sometimes  advisable  to  learn  whether  or 
not  there  is  carbon  dioxid  in  the  well  by  lowering  a  lantern  into  it.  If  carbon 
dioxid  is  present  in  large  quantities,  the  lantern  will  go  out.  Why  ? 


ISO  HUMAN  PHYSIOLOGY 

Amount  of  Fresh  Air  needed.  To  keep  the  amount  of  car- 
bon dioxid  in  the  air  from  becoming  too  great,  a  man  must 
have  3000  .cubic  feet  of  fresh  air  every  hour.  If  he  is 
working,  he  will  need  twice  this  amount.  An  eight-year-old 
boy  needs  one  half  as  much  as  a  man. 

Usually  it  is  not  possible  to  change  the  air  of  a  room  more 
than  five  times  an  hour  without  causing  drafts.  Changing  it 
five  times  an  hour,  each  person  must  have  600  cubic  feet  of 
air  space  in  a  room  to  get  his  3000  cubic  feet  of  fresh  air. 
Public  buildings,  therefore,  should  have  600  cubic  feet  of  air 
space  for  each  person,  and  in  the  living  and  sleeping  rooms 
of  private  dwellings,  each  member  of  the  family  should  have 
1000  cubic  feet  of  space.1  Of  course,  even  with  this  much 
space,  the  air  will  become  bad  unless  there  is  some  way  of 
constantly  changing  it. 

How  to  tell  when  the  Air  in  a  Room  is  Bad.  All  of  us  suffer 
more  or  less  from  carbon  dioxid  poisoning,  and  ventilation  is 
probably  the  most  important  of  all  the  problems  of  hygiene. 
It  is,  therefore,  very  important  for  us  to  be  able  to  tell  when 
the  air  in  a  room  is  bad.  One  fairly  good  way  of  doing  this 
is  by  the  nose.  If  the  air  in  a  room  smells  close  when  one 
comes  in  from  outdoors,  the  ventilation  is  not  sufficient. 
After  staying  in  a  badly  ventilated  room  for  a  time,  the  smell 
of  bad  air  is  not  noticed,  but  after  one  has  been  out  in  the 
fresh  air,  the  nose  is  a  fairly  good  judge  of  the  quality  of  air. 

Principles  of  Ventilation.  A  room  will  hold  only  a  certain 
amount  of  air,  and  if  fresh  air  is  brought  in,  part  of  the  air 
already  in  the  room  must  pass  out.  In  any  system  of  venti- 

1  Lamps  and  gas  jets  give  off  carbon  dioxid,  and  where  these  are  burning,  an 
extra  supply  of  air  is  needed.  Oil  stoves  and  gas  stoves  that  are  not  connected 
with  a  chimney  are  exceedingly  unhealthful,  for  they  give  off  large  quantities  of 
carbon  dioxid  into  the  air  of  the  room. 


VENTILATION  l8l 

lation  there  must,  therefore,  be  an  opening  through  which  the 
air  can  enter  the  room,  and  an  opening  through  which  it  can 
escape.  Carbon  dioxid  is  heavier  than  the  other  gases  of 
the  air,  and  in  the  air  of  a  room  it  sinks  toward  the  floor.  The 
opening  by  which  the  air  passes  out  of  the  room  should,  there- 
fore, be  near  the  floor. 

In  ordinary  buildings  some  air  finds  its  way  through  crevices 
around  windows  and  doors  and  through  the  floors.  Opening 
and  closing  doors,  and  persons  passing  in  and  out  of  a  room, 
also  create  a  circulation  of  the  air.  Air  may  pass  both  out 
and  in  through  the  same  opening,  as  you  can  show  by  the 
following  experiment : 

Hold  a  lighted  candle  near  the  top  of  an  open  doorway.  The  candle 
flame  will  be  blown  to  one  side,  showing  that  a  current  of  air  is  passing 
in  or  out  through  the  top  of  the  doorway.  Now  hold  the  candle  in  the 
doorway  close  to  the  floor.  The  air  current  here  will  usually  be  found 
to  be  passing  in  a  direction  opposite  to  the  direction  of  the  current 
of  air  in  the  top  of  the  doorway.  '  By  holding  the  candle  at  different 
heights,  find  a  stationary  layer  of  air  lying  between  two  layers  of  air 
that  are  moving  in  opposite  directions.  Open  or  close  some  other 
door  of  the  room  and  note  the  effect  on  the  candle  flame.  Have 
some  one  walk  through  the  doorway  past  the  flame  and  note  the 
effect. 

Ventilating  Public  Buildings.  In  many  public  buildings  it  is 
impossible  to  have  satisfactory  ventilation,  because  the  builders 
did  not  provide  any  special  arrangements  for  drawing  off  the 
used  air  and  for  sending  in  a  supply  of  fresh  air.  Windows 
were  put  in  houses,  not  to  be  used  as  ventilators,  but  to 
admit  light,  and  it  is  very  difficult  to  use  them  as  ventilators 
without  causing  drafts.  In  schoolhouses,  churches,  theaters, 
and  other  buildings,  where  many  people  collect,  some  way  of 
forcing  in  fresh  air  and  of  drawing  off  the  air  which  has 
been  used,  should  be  provided.  Unless  this  is  done,  it  is 


182 


HUMAN  PHYSIOLOGY 


almost  impossible  in  cold  weather  to  change  the  air  rapidly 
enough  to  prevent  carbon  dioxid  from  accumulating  in  the 
building. 

Heating  Systems  and  Ventilation.  Heating  with  a  hot-air 
furnace  is  healthful,1  for  a  furnace  constantly  sends  a  supply 
of  fresh  air  into  the  room.  A  fireplace  gives  considerable 


FIG.  88.  How  a  fireplace  helps  to  ventilate  a  room.  A  current  of  air  passes  up 
the  chimney,  and  this  causes  the  fresh  air  to  be  drawn  into  the  room. 

ventilation  by  causing  a  draft  of  air  up  the  chimney.  Stoves 
give  some  ventilation  in  the  same  way,  but  not  so  much  as  an 
open  fire.  Radiators  heated  by  hot  water  and  steam  give 
no  ventilation. 

Avoiding  Drafts.  The  great  problem  connected  with  venti- 
lation is  how  to  get  the  fresh  air  into  the  room  without  causing 
cold  drafts.  One  of  the  most  satisfactory  ways  of  doing  this 
is  to  have  warm  air  sent  in  by  the  heating  system.  Some 

1  Some  cheap  iron  furnaces,  when  they  become  red  hot,  allow  gas  from  the 
coal  to  pass  through  them.  Breathing  this  gas  is  exceedingly  unhealthful. 


VENTILATION 


183 


very  useful  devices  for  ventilating  are  made,  by  which  air  is 

drawn  in  behind  a  fireplace  or  into  a  jacket  around  a  stove 

and  warmed  before  it  comes  into 

the  room.     A  board  set  under  a 

window  sash  allows  the  air  to  come 

in  between  the  two  sashes  and  go 

upward  without  causing  a  draft  on 

those  sitting  in  the  room.     You  can 

still  further  improve  on  this  kind  of 

ventilator  by  cutting  two  or  three 

holes  in  the  board  and  boxing  them 

in,  as  shown  in  Figure  89. 

Even  when  buildings  have  been 
constructed  with  no  ventilating  sys- 
tem, it  is  possible  to  do  much  to 
secure  fresh  air  without  causing 
harmful  drafts.  Several  windows 
may  each  be  opened  a  little,  when 
to  open  one  wide  would  cause  great  trouble.  Schoolrooms 
and  churches  should  be  filled  with  fresh  air  while  they  are 
empty.  At  noon  and  during  recesses  schoolroom  windows 
can  be  opened  and  a  great  deal  done  in  a  very  short  time 
toward  getting  out  the  stale  air. 

Importance  of  ventilating  Sleeping  Rooms.  A  great  deal 
of  time  is  spent  in  the  atmosphere  of  the  sleeping  room,  and 
at  night  the  air  of  sleeping  rooms  is  not  set  in  motion  by  the 
opening  and  closing  of  doors  and  by  persons  passing  out  and 
in.  For  these  reasons  the  ventilation  of  the  room  where  you 
sleep  deserves  special  attention. 

If  your  sleeping  room  is  not  ventilated  in  some  other  way, 
you  should  open  one  or  more  windows  each  night.  If  the 
windows  are  so  arranged  that  they  cannot  be  opened  without 


FIG.  89.    Ventilating  by  placing 
a  board  under  a  window. 


1 84  HUMAN  PHYSIOLOGY 

causing  a  draft  over  the  bed,  fit  boards  under  the  sashes, 
or  get  fresh  air  in  some  other  way.  Do  not  sleep  in  a 
closed  room  breathing  again  and  again  the  carbon  dioxid 
that  has  come  off  from  your  own  lungs,  and  do  not  be  afraid 
to  admit  the  night  air  to  your  room,  for  the  same  atmos- 
phere that  surrounds  houses  during  the  day  surrounds  them 
at  night. 

Outdoor  Sleeping.  Every  year  more  and  more  people  are 
sleeping  outdoors.  It  was  long  ago  noticed  that  people  who 
lived  much  in  the  open  air  were  not  troubled  with  consumption 
as  were  those  who  lived  indoors.  Then  it  was  found  that 
sleeping  outdoors  often  helped  to  cure  consumption.  People 
began  to  wonder  why  anything  that  helped  to  cure  sick- 
ness might  not  also  help  to  keep  them  from  getting  sick, 
so  more  and  more  of  them  are  building  upper  porches 
and  other  places  where  they  can  conveniently  sleep  in  the 
open  air. 

It  is  probable  that  the  benefits  of  outdoor  sleeping  come 
from  spending  the  long  time  when  one  is  in  bed  in  an 
atmosphere  that  is  as  free  as  possible  from  carbon  dioxid. 
With  this  amount  of  time  spent  in  the  pure  outdoor  air, 
the  body  becomes  so  well  and  strong  that  it  can  kill  off 
the  disease  germs  that  get  into  it.  A  well-ventilated  house 
helps  to  preserve  the  health ;  walking  and  other  exercises 
that  require  spending  time  in  the  open  air  are  also  healthful ; 
but  outdoor  sleepers  think  their  way  of  obtaining  fresh  air  is 
the  best  of  all,  because  in  this  way  most  of  them  spend  more 
time  in  the  outdoor  air  than  they  could  possibly  do  in  any 
other  way. 

Summary.  The  lack  of  fresh  air  is  the  greatest  evil  that 
accompanies  indoor  life.  Oxygen  and  carbon  dioxid  are  the 
important  gases  of  the  air  from  the  standpoint  of  the  health 


VENTILA  TION  1 8  5 

Ten  per  cent  of  oxygen  is  enough  for  the  body,  so  we  rarely 
suffer  because  there  is  not  enough  oxygen  in  the  air.  The 
carbon  dioxid  is  poisonous  to  the  human  body,  and  to  get 
rid  of  it  is  the  problem  of  ventilation.  Each  person  should 
have  600  cubic  feet  of  room  space  and  3000  cubic  feet  of 
fresh  air  per  hour.  It  is  especially  important  that  the  sleep- 
ing room  be  well  ventilated,  because  much  time  is  passed  in 
the  atmosphere  of  this  room.  Outdoor  sleeping  is  a  healthful 
practice  which  is  probably  beneficial  because  it  furnishes  the 
sleeper  with  plenty  of  fresh  air. 

QUESTIONS 

Of  what  two  gases  is  the  air  chiefly  composed  ?  Name  one  other 
gas  that  is  found  in  small  quantities  in  the  air.  What  per  cent  of 
the  air  is  oxygen  ?  What  per  cent  of  expired  air  is  oxygen  ?  What 
per  cent  of  carbon  dioxid  is  in  ordinary  air  ?  in  expired  air  ?  What 
is  the  effect  of  breathing  a  small  amount  of  carbon  dioxid  ?  of  long- 
continued  breathing  of  carbon  dioxid?  of  breathing  large  quantities 
of  carbon  dioxid  ?  What  do  miners  call  carbon  dioxid  ? 

How  much  fresh  air  is  needed  by  a  man  when  he  is  at  rest  ?  by 
a  working  man?  by  a  boy?  In  public  buildings,  how  much  space 
should  there  be  for  each  person?  in  sleeping  rooms?  Why  is  more 
air  needed  where  lamps  or  gas  jets  are  burning?  How  can  one  tell 
when  the  air  in  a  room  is  bad? 

In  ventilating,  why  should  the  opening  by  which  the  air  passes  out 
be  near  the  floor?  What  is  necessary  for  the  satisfactory  ventilation 
of  crowded  public  buildings?  What  systems  of  heating  ventilate  a 
room?  What  systems  give  no  ventilation?  Explain  how  a  fireplace 
or  stove  brings  fresh  air  into  a  room.  Give  some  ways  of  avoiding 
drafts  in  ventilation.  What  should  be  done  while  schoolrooms  and 
churches  are  empty?  Why  should  sleeping  rooms  be  especially  well 
ventilated?  Is  night  air  unhealthful?  From  what  do  the  benefits  of 
outdoor  sleeping  probably  come  ? 


CHAPTER    XIV 


RENAL  ARTERY 


THE   KIDNEYS   AND   THE   BODY  WASTES 

SOMETIMES  the  body  is  well ;  sometimes  it  becomes  ill. 
Why  is  it  strong  and  abounding  in  health  at  one  time  and  at 
another  time  weak  and  ill  ?  Usually  not  because  it  lacks 
food  or  oxygen,  or  because  it  is  too  hot  or  too  cold,  but  be- 
cause there  are  poisons  in  the  body  that  injure  tJie  cells. 

Sometimes  the  poisons  that  cause 
sickness  are  produced  by  disease 
germs  (page  285).  Frequently  they 
come  from  our  own  cells.  Our 
bodies  constantly  produce  carbon 
dioxid  and  poisonous  proteid  wastes 
(urea  and  uric  acid),1  and  without 
organs  for  throwing  off  these  sub- 
stances, life  for  us  would  not  be 
possible  for  even  an  hour.  We 
have  already  learned  how  the  car- 
bon dioxid  is  excreted  from  the 
body.  In  this  chapter  we  shall 
study  the  kidneys,  —  the  organs  that 
remove  the  uric  acid  and  urea  from 
the  blood. 

The  Kidneys.  The  kidneys  are 
two  bean-shaped  organs.  They  are 
fastened  to  the  back  wall  of  the 


FIG.  90.     The   kidneys   and 
the  bladder  as  seen  from  behind. 


1  There  are  other  proteid  wastes  besides  the  urea  and  uric  acid,  but  for  the 
sake  of  convenience  the  others  will  be  disregarded  here. 

1 86 


THE  KIDNEYS  AND   THE  BODY  WASTES 


I87 


abdominal  cavity,  one  on  either  side  of  the  spinal  column. 
Stored  around  the  kidneys  are  great  quantities  of  fat.  The 
function  of  the  kidneys  is  to  excrete  urea,  tiric  acid,  and  water. 
As  the  lungs  purify  the  blood  by  removing  from  it  carbon 
dioxid,  so  the  kidneys  purify  the  blood  by  taking  out  of  it 
urea  and  uric  acid. 


FIG.  91.  A  is  a  longitudinal  section  of  a  kidney,  showing  how  the  kidney  tubules 
empty  into  the  branches  of  the  ureter.  B  is  a  kidney  tubule  enlarged  to  show  the  cor- 
puscle at  its  upper  end,  and  the  long,  winding  course  the  tubule  follows  before  it 
empties  into  the  ureter.  Cis  a  small  portion  of  a  tubule,  showing  how  the  walls  of  the 
tubule  are  built  of  cells. 

The  Tubules  of  the  Kidneys.  The  kidneys  are  composed 
chiefly  of  an  enormous  number  of  very  fine  winding  tubes 
(tubules).  The  tubules  rise  in  little  sacs  (Fig.  91  B)  and  flow 


i88 


HUMAN  PHYSIOLOGY 


together,  forming  larger  tubules.  These  larger  tubules  all 
run  to  the  inner  side  of  the  kidney,  where  they  empty  into 
the  branches  of  the  ureter  (Fig.  91  A). 

The  Renal  Corpuscles.  The  corpuscle  on  the  end  of  a 
kidney  tubule  consists  of  a  double-walled  sac  and  a  tuft  of 
blood  vessels.  The  structure  of  a  corpuscle  is  most  easily 
learned  by  studying  its  development. 

When  the  kidney  is  being  formed  in  a  very  young  animal, 
the  kidney  cells  arrange  themselves  so  as  to  form  tubes 


FlG.  92.     The  development  of  a  renal  corpuscle.      The  corpuscle  is  formed  by  a 
blood  vessel  pushing  in  the  end  of  a  kidney  tubule.     (After  Bailey.) 

(Fig.  91  C).  A  small  blood  vessel  grows  up  close  against  the 
end  of  a  tube  (Fig.  92  A)  and  begins  to  push  it  in  (Fig.  92  B). 
The  end  of  the  tube  then  broadens  out  and  forms  a  small  round 
sa'c,  which  grows  up  around  the  blood  vessel  (Fig.  92  C). 
Meanwhile,  the  blood  vessel  twists  about  and  divides  up  into 
capillaries,  and  continues  pushing  in  the  wall  of  the  sac 
(Fig.  92  D  and  E\  until  at  last  the  corpuscle  consists  of  a 
bunch  of  little  blood  vessels  buried  in  a  narrow-mouthed 
pocket  in  the  end  of  the  sac.  This  pocket  almost  fills  the 
sac  (Fig.  91  B). 


THE  KIDNEYS  AND    THE  BODY  WASTES          189 

How  the  Wastes  are  excreted  from  the  Kidneys.  When 
the  blood  is  flowing  through  the  capillaries  in  a  renal  cor- 
puscle, the  wastes  escape  through  the  capillary  walls.  They 
then  pass  on  through  the  inner  walls  of  the  sac  into  the  tubule, 
and  flow  down  the  tubule  to  the  ureter.  Also,  blood  capilla- 
ries are  abundant  all  through  the  kidneys,  and  along  the 
course  of  the  tubules,  wastes  from  the  blood  pass  into  the 
tubules  tJirough  the  tubule  walls.  Drop  by  drop  the  millions 
of  kidney  tubules  separate  the  wastes  from  the  blood  and 
empty  them  into  the  ureters,  which  carry  the  wastes  to  the 
bladder. 

Alcohol  and  the  Kidneys.  More  commonly,  probably,  than 
any  other  organs  of  the  body,  the  kidneys  become  diseased 
from  alcohol  drinking.  The  cells  in  the  corpuscles  and 
tubules  of  the  kidneys  should  allow  the  wastes  to  pass 
through  them,  and  at  the  same  time  they  should  hold  back 
the  food  that  is  dissolved  in  the  blood.  Alcohol  may  cause 
the  kidney  cells  to  become  diseased  and  to  allow  the  foods  to 
escape  with  the  wastes.  Sometimes  the  cells  suffer  from 
fatty  degeneration,  and  still  more  commonly  the  connective 
tissue  in  the  kidney  increases  greatly  (page  102)  and  stran- 
gles the  cells  of  the  tubules.  In  Bright's  disease,  which  is 
much  more  common  among  alcohol  drinkers  than  among 
abstainers,  whole  tubules  die  and  the  proteid  foods  are 
allowed  to  escape  with  the  wastes. 

Summary.  Ill  health  is  often  the  result  of  poisoning  of 
the  cells.  The  kidneys  are  organs  for  removing  the 
poisonous  proteid  wastes  and  water  from  the  body.  A 
kidney  is  composed  of  many  fine  tubules,  each  of  which  ends 
in  a  renal  corpuscle.  A  tuft  of  blood  capillaries  is  buried  in 
each  of  the  corpuscles  and  the  wastes  pass  out  from  the 
blood  into  the  tubules  and  down  to  the  ureters.  Alcohol 


190  HUMAN  PHYSIOLOGY 

causes  kidney  trouble,  Bright's  disease  being  very  common 
among  drinkers. 

QUESTIONS 

To  what  is  ill  health  frequently  due?  Where  do  these  poisons 
come  from  ?  Locate  the  kidneys.  What  is  deposited  around  them  ? 
What  is  their  function  ? 

Of  what  is  a  kidney  chiefly  composed?  Describe  the  course  of 
the  tubule.  In  what  does  a  tubule  rise  ?  Describe  the  development 
and  structure  of  a  renal  corpuscle.  How  do  the  wastes  get  from  the 
blood  into  the  tubules? 

What  should  the  cells  of  the  kidney  tubules  do  with  the  wastes  and 
with  the  foods?  What  two  diseased  conditions  of  the  kidneys  does 
alcohol  cause?  What  disease  of  the  kidneys  is  common  among 
drinkers  ? 


CHAPTER  XV 


THE  SKIN  AND  THE  BODY  HEAT 


The  Functions  of  the 
Skin.  The  skin  has  four 
functions.  It  forms  a 
protective  covering  for  the 
body,  which  keeps  the 
more  delicate  tissues  from 
being  injured,  and  pre- 
vents disease  germs  from 
getting  in  among  them. 
It  is  an  organ  of  feeling, 
for  most  of  the  nerves  of 
touch  end  in  the  skin.  // 
regulates  the  heat  of  the 
body,  permitting  the  body 
to  cool  off  when  it  be- 
comes too  warm,  and 


-DERMIS 
BLOOD  VESSEL 


FIG.  93.    A  section  of  the  skin.    B  is  a  small 


keeping  in  the  heat  when       portion  of  a  sweat  gland,  and  Cis  a  cross-section 
the    body    becomes    COld.        of  a  sweat  Sland  enlarged  to  show  that  these 


Its  other   function  is    to 


glands  are  hollow  tubes  with  walls  composed  of 
cells. 

assist  the  lungs  and  kid- 
neys in  excreting  water^  from  the  body.     The  skin  has  two 
layers,  the  epidermis  and  the  dermis. 

1  The  lungs,  kidneys,  and  skin  give  off  so  much  water  that  we  are  compelled 
to  drink  liquids  to  give  the  body  a  sufficient  supply  of  water.  You  should  under- 
stand, therefore,  that  when  the  skin  excretes  water,  the  object  is  to  cool  the  body 
and  not  to  get  rid  of  the  water. 

191 


192 


HUMAN  PHYSIOLOGY 


Thickening  of  the  Epidermis.     The 

epidermis  is  the  protective  layer  of  the 
skin,  and  wherever  unusual  pressure 
comes  on  the  skin,  as  on  the  soles  of 
the  feet  or  on  the  palms,  the  epider- 
mal cells  multiply  very  rapidly  and 
cause  a  great  thickening  of  the  outer 
layer  of  the  epidermis.  When  con- 
stant pressure  falls  on  a  small  area 
of  epidermis,  as  sometimes  happens 
when  a  tight  shoe  is  worn,  a  corn,  or 
little  mound  of  epidermal  cells,  is  built 
up.  This  can  be  relieved  only  by  re- 
moving the  pressure  that  caused  the 
growth.  It  is  much  easier  to  prevent 
sorns  than  it  is  to  cure  them,  and  only 
properly  fitting  shoes  should  be  worn.1 
A  wart  is  a  place  where  the  epidermal 
cells  grow  and  multiply  more  than  is 
~  „  natural,  but  the  cause  of  warts  is  not 

FlG.  94.     A  section  of  the 

epidermis.      The    epidermis    known.     In  cancer,  either  the  epider- 
grows  by  the  division  of  the    mai  ceus  or  the  connective  tissue  cells 

lower  cells.    Its  outer  cells  dry      .  .  .     .       , •"  3 

and  scale  off.   A  papilla  con-    increase  enormously  and  feed  on  the 

taining    a  touch    corpuscle  is      Other  body  tissues. 

The  Color  of  the  Skin.  The  color 
of  the  skin  is  due  to  pigment  in  the 
cells  of  the  lower  layers  of  the  epidermis.  The  outer  epider- 
mal layers  are  partially  transparent,  and  we  look  through 
these  and  see  the  coloring  matter  in  the  lower  cells.  Expos- 

1  It  is  estimated  that  58  per  cent  of  Americans  have  corns,  ingrowing  nails,  the 
bones  of  the  feet  bent  out  of  shape,  or  other  foot  troubles.  The  question  of 
properly  fitting  shoes  is,  therefore,  one  of  considerable  importance. 


shown.     The  skin  pigment  is  in 
the  lower  cells  of  the  epidermis. 


THE  SKI  AT  AND   THE  BODY  HEAT 


193 


The  subcutaneous 


ure  to  the  sun  or  wind  causes  the  coloring  matter  to  become 
more  abundant  in  the  skin,  and  the  skin,  as  we  say,  becomes 
tanned.  A  freckle  is  a  spot  in  the  epidermis  where  the  pig- 
ment is  especially  abundant.  It  is  probable  that  the  use  of 
the  skin  pigment  is  to  protect  the  nerves  and  other  delicate 
structures  beneath  the  epidermis  from  the  light  of  the  sun. 

The  Dermis  and  the  Subcutaneous  Layer.  The  second 
layer  of  the  skin  is  the  dermis.  It  is  composed  of  connec- 
tive tissue  in  which  there  are  blood  vessels,  lymphatic  vessels, 
and  nerves.  The  upper  surface  of  the  dermis  is  thrown  into 
papillce  that  stand  up  like  little  mountain  peaks  under  the 
epidermis.  Some  of  the  papillae  contain  blood  vessels,  and 
some  of  them  contain  touch  corpuscles.  In  the  lower  part 
of  the  dermis  considerable  fat  is  stored. 
layer  lies  under  the  dermis.  It  is  a 
layer  of  loose  connective  tissue  in 
which  large  quantities  of  fat  are  found. 

Sweat  Glands.  With  a  magnifying 
glass  small  pores  can  be  seen  in  the 
skin,  in  some  portions  of  the  body  as 
many  as  twenty-five  hundred  to  the 
square  inch.  They  are  the  mouths  of 
sweat  glands,  which  are  little  tubes 
composed  of  epidermal  cells  (Fig.  93). 

FIG.  95.    The   surface    of 

A  sweat  gland  runs  down  through  the  the  skin  of  the  finger-tip,  mag- 
epidermis  and  ends  in  a  coil  in  the  nified  to  show  lhe  mouths  of 

i  f     ,t          -i  ,1         the  sweat  glands.     In  some 

lower  part  of  the  dermis,  or  m  the  parts  of  theg  skin  the  papilte 
subcutaneous  layer. 

The  Function  of  the  Sweat  Glands. 
TJie  function  of  the  sweat  glands  is  to 
cool  the  body  by  pouring  out  perspiration  on  the  skin.     Around 
the  lower  part  of  a  sweat  gland  are  many  fine  blood  capillaries 


are  arranged  in  rows,  giving 
the  surface  of  the  ski»  a 
ridged  appearance. 


IQ4  HUMAN  PHYSIOLOGY 

from  which  an  abundant  supply  of  lymph  escapes.  The  water 
of  the  lymph  passes  on  through  the  walls  of  the  sweat  gland 
into  the  opening  in  the  center  of  the  gland,  and  flows  out  on 
the  skin.  A  little  perspiration  passes  out  through  the  sweat 
glands  at  all  times,  but  usually  the  amount  is  so  small  that  it 
passes  off  into  the  air  as  vapor  without  being  noticed.  On  a 
hot  day,  however,  or  when  the  body  becomes  hot  from 
exercise,  the  sweat  glands  work  so  rapidly  that  the  water 
accumulates  on  the  skin. 

How  the  Body  is  cooled  by  the  Perspiration.  The  body  is 
cooled  by  the  evaporation  of  the  perspiration  on  the  skin. 
Pour  alcohol  or  ether  on  your  hand  and  allow  it  to  evaporate 
and  your  hand  will  feel  cold.  This  shows  that  a  liquid  in 
evaporating  takes  up  heat.  You  can  have  the  same  fact 
proved  to  you  by  visiting  an  ice  factory  and  seeing  water 
frozen  by  the  evaporation  of  ammonia,  or  by  performing  the 
following  experiment : 

Note  the  height  at  which  the  mercury  stands  in  a  thermometer. 
Then  cover  the  bulb  of  the  thermometer  with  cotton,  and  wet  the 
cotton  with  ether,  chloroform,  benzine,  gasoline,  or  alcohol.  Swing 
the  thermometer  through  the  air  and  then  note  the  height  of  the 
mercury.  What  causes  it  to  fall  ? 

The  Sweat  Glands  controlled  by  the  Nervous  System.  The 
sweat  glands  are  controlled  by  the  nervous  system,  which 
causes  them  to  work  rapidly  or  slowly  according  to  the  heat 
of  the  body.  That  the  sweat  glands  are  connected  with  the 
nervous  system  is  shown  by  the  way  embarrassment  or  pain 
may  bring  out  the  perspiration. 

The  Hair.  A  hair  grows  in  a  small,  deep  pocket  in  the 
skin,  called  the  hair  follicle.  At  the  bottom  of  the  follicle  is 
the  hair  papilla.  This  is  a  little  mound  of  connective  tissue, 
belonging  to  the  upper  layer  of  the  dermis.  The  follicle  is 


THE  SKIN  AND    THE  BODY  HEAT 


195 


lined  with  and  the  hair  papilla  is  covered  over  by  cells  which 
have  been  folded  in  from  the 
epidermis.  The  hair  rests 
on  the  papilla,  and  grows  by 
the  epidermal  cells  at  the 
base  of  the  hair  multiplying 
and  pushing  the  cells  above 
them  upward.  A  hair,  like 
the  epidermis,  contains  nei- 
ther nerves  nor  blood  vessels. 
In  the  connective  tissue  of 
the  papilla,  however,  is  a  rich 
blood  supply,  which  brings 
food  to  the  growing  'cells  at 
the  base  of  the  hair. 

The  Sebaceous  Glands  and 
the  Muscles  of  the  Hair. 
Opening  off  from  the  sides 
of  the  hair  follicles  are  the 
sebaceous  glands,  which  man- 
ufacture a  clear,  odorless  oil 
for  the  hair.  Small  muscles  * 
are  attached  to  the  hair  folli- 
cle in  such  a  way  that  when 


FIG.  96. 


BLOOD  VESSEL 

A  hair  in  its  follicle. 


they  contract,  the  hair  is  made  to  stand  on  end.  Doubtless 
you  have  seen  the  hairs  on  a  cat's  tail  or  on  a  dog's  neck  stand 
on  end,  and  you  probably  know  that  in  man  great  fright  may 
cause  these  muscles  to  contract  and  make  the  hair  stand  up. 

1  The  upper  ends  of  these  muscles  are  attached  in  the  connective  tissue  just 
below  the  epidermis.  Under  certain  conditions  they  contract  and  draw  the  epi- 
dermis down  in  little  depressions,  producing  the  condition  that  is  called  "  goose- 
flesh." 


196  HUMAN  PHYSIOLOGY 

Care  of  the  Hair.  Brushing  the  hair  is  very  beneficial  to  it 
because  it  spreads  the  oil  from  the  sebaceous  glands  all  along 
the  hair.  Brushing  the  hair  also  causes  a  good  circulation  of 
blood  in  the  scalp,  thus  providing  the  growing  cells  of  the 
hair  with  an  abundance  of  food  and  oxygen,  and  promptly 
carrying  away  their  wastes.  The  hair  and  scalp  should  be 
washed  occasionally  with  good  soap  to  remove  dust  and  oil. 
A  little  ammonia  or  borax  in  the  water  is  useful  when  the 
hair  is  very  oily,  but  if  this  treatment  causes  the  hair  to 
become  dry  and  brittle,  only  soap  and  water  should  be  used. 

Dandruff  and  Baldness.  It  is  thought  that  dandruff  is 
caused  by  a  germ  that  grows  in  the  sebaceous  glands  and 
the  scalp,  and  that  this  disease  may  be  spread  by  hair  brushes 
and  combs.  It  is,  therefore,  safest  not  to  use  the  combs  and 
brushes  that  are  found  in  public  places. 

Baldness  is  supposed  usually  to  be  caused  either  by  dan- 
druff or  by  tight  hats  that  cut  off  the  blood  from  the  scalp. 
Notice  persons  who  are  bald  and  you  will  find  that  usually 
the  bald  part  of  the  head  is  the  part  that  is  covered  by  the 
hat.  When  a  hair  falls  out,  a  new  hair  will  take  its  place,  pro- 
vided the  epidermal  cells  that  line  the  lower  part  of  the  hair 
follicle  and  cover  the  hair  papilla  are  not  destroyed.  If  these 
are  destroyed,  the  hair  will  not  be  renewed. 

The  Nails.  A  nail  is  formed  from  the  upper  horny  layer 
of  the  epidermis.  Its  growth  is  chiefly  at  the  base,  as  you 
will  know  if  you  have  seen  a  spot 1  grow  forward  on  a  nail 
until  it  reached  the  tip.  The  nail  cells  turn  to  a  horny  sub- 
stance, and  the  nails  have  a  pink  appearance  because  the  rich 
blood  supply  below  can  be  seen  through  them.  Where  the 
cells  are  young,  the  blood  cannot  be  seen  so  plainly  through 

1  A  black  spot  on  a  nail  is  caused  by  injuring  the  blood  vessels  under  the  nail, 
thus  allowing  the  blood  to  flow  out  and  form  a,  clot. 


THE  SKIN  AND   THE  BODY  HEAT  197 

them,  and  there  is,  therefore,  a  white  area  at  the  base  of  each 
nail. 

When  a  nail  is  injured,  or  lost  through  accident,  it  will 
grow  again,  provided  the  bed  of  epidermal  cells  on  which  the 
nail  rests  and  from  which  it  grows  is  not  destroyed.  But  if 
the  "  roots  of  the  nail "  are  destroyed,  the  nail  will  not  be  re- 
placed. The  nails  protect  the  fingers,  and  assist  in  picking 
up  small  objects. 

THE  BODY   HEAT 

A  man  in  the  cold  Arctics  loses  much  more  heat  than  does 
a  man  living  in  the  warm  tropics.  Yet  the  temperature  of  the 
human  body  all  over  the  world  is  the  same.  A  man  who  is 
violently  exercising  produces  five  or  six  times  as  much  heat 
as  a  resting  man  produces.  Yet  the  temperature  of  the 
human  body  in  exercise  and  rest  is  nearly  the  same.  In 
health,  the  human  body  keeps  a  temperature  of  about  98 \ 
degrees,  varying  only  about  one  half  of  a  degree  above  or 
below  this  point. 

The  Regulation  of  the  Body  Heat.  On  a  cold  day  we  can 
close  the  doors  and  windows  of  a  room  and  with  a  small  fire 
keep  the  temperature  of  the  room  at  70  degrees,  or  we  can 
open  a  window  and  still  keep  the  temperature  of  the  room  at 
70  degrees  by  firing  up  and  producing  more  heat.  We  can 
control  the  temperature  of  the  room  either  through  the 
amount  of  heat  that  is  lost,  or  through  the  amount  of  heat 
that  \s  produced.  So  the  temperature  of  the  human  body  can 
be  kept  at  98 1  degrees  either  by  regulating  the  amount  of 
heat  that  escapes  from  tJie  body,  or  by  regulating  the  amount 
of  heat  produced  in  the  body.  Both  of  these  methods  are 
used  in  our  bodies. 


198  HUMAN  PHYSIOLOGY 

Regulating  the  Escape  of  Heat  The  skin  governs  the 
escape  of  heat  from  the  body  in  two  ways.  The  first  way 
is  by  regulating  tJie  amount  of  blood  tJiat  comes  out  into  tJie 
skin.  When  the  body  is  cold,  the  blood  vessels  of  the  skin 
contract  and  keep  the  blood  in  the  warm  internal  parts  of 
the  body.  When  the  body  is  hot,  the  vessels  in  the  skin  open 
up  and  allow  a  larger  amount  of  blood  to  come  to  the  outside 
of  the  body  where  it  will  be  cooled. 

The  other  method  of  regulating  the  escape  of  the  heat  is 
through  the  sweat  glands.  When  the  heat  of  the  body  rises, 
the  sweat  glands  cool  the  body  by  pouring  out  perspiration 
on  the  skin.  Both  the  vessels  of  the  skin  (page  145)  and  the 
sweat  glands  are  governed  by  the  nervous  system,  so  it  is  the 
nervous  system  that  regulates  the  amount  of  heat  that  escapes 
from  the  body. 

Regulating  the  Amount  of  Heat  produced.  When  the  body 
is  exposed  to  severe  cold,  much  heat  escapes  from  it,  and  the 
cells  burn  an  extra  supply  of  food  to  keep  the  body  tempera- 
ture up  to  98^-  degrees.  For  this  reason,  men  living  outdoors 
in  cold  weather  require  great  quantities  of  food  (page  124). 
For  the  same  reason,  an  animal  that  is  kept  outdoors  in  the 
winter  needs  more  food  than  the  same  animal  requires  when 
it  is  kept  in  a  warm  stable. 

The  Temperature  of  the  Body  in  Illness.  When  one  is  weak 
and  ill,  the  body  temperature  sometimes  falls  below  normal, 
not  enough  heat  being  produced  or  too  much  heat  being  lost. 
Sometimes  the  sweat  glands  work  when  they  should  not  do 
so,  as  in  the  night  sweats  which  accompany  consumption  and 
other  weakening  diseases.  More  commonly  the  temperature 
rises  above  98 \  degrees,  when  one  is  said  to  have  fever. 

The  Cause  of  Fever.  In  fever  there  is  usually  a  greater 
breaking  down  of  the  tissues  and  a  greater  production  of 


THE  SKIN  AND   THE  BODY  HEAT  199 

heat  than  is  natural.  Not  nearly  so  much  heat  is  produced 
in  fever,  however,  as  in  violent  exercise,  and  the  main  cause 
of  a  fever  is  that  not  enough  heat  is  lost.  Usually  the  trouble 
is  that  tJie  sweat  glands  refuse  to  work.  The  crisis  or  turn 
of  a  fever  is  usually  marked  by  the  sweat  glands  beginning 
their  work,  the  surplus  heat  escaping  and  the  fever  going 
down  from  that  time.1 

Chills.  In  illness  the  skin  usually  is  hot  and  flushed  with 
blood,  but  sometimes  the  blood  vessels  of  the  skin  are  tightly 
closed  and  the  blood  is  kept  from  coming  to  the  outside  of 
the  body  where  it  will  be  cooled.  Then  the  skin  has  no 
warm  blood,  and  the  person  has  a  chill  and  feels  cold,  even 
when  the  inner  parts  of  the  body  are  in  a  hot  fever. 

The  Extremes  of  Body  Temperature.  The  human  body  is 
very  sensitive  indeed  to  changes  in  temperature,  and  will  die 
if  its  heat  falls  far  below  or  rises  much  above  normal.  One 
hundred  and  two  degrees  is  warm  fever,  and  104  degrees  is 
a  hot  fever;  105  degrees,  if  it  continues  for  long,  is  danger- 
ous, and  when  a  fever  rises  to  109  or  1 10  degrees,  it  is  almost 
surely  fatal.  How  far  below  normal  the  temperature  can 
fall  without  fatal  results  depends  on  how  long-continued  the 
decline  is,  but  91  or  92  degrees  will  cause  death  in  a  very 
short  time. 

1  Sometimes,  in  slight  fevers,  a  hot  bath,  followed  by  an  extra  heavy  covering 
of  the  body  for  a  time,  will  start  the  sweat  glands  and  lower  the  fever.  Rubbing 
with  alcohol  quickly  cools  the  body,  because  the  alcohol  evaporates  very  rapidly. 
Sponging  with  water  cools  the  skin  in  the  same  way,  but  not  so  rapidly.  Some- 
times, in  long-continued  illness,  where  the  temperature  goes  so  high  that  there  is 
danger  of  death  from  the  fever,  it  is  best  to  take  the  heat  out  of  the  body  with 
ice  packs  or  an  ice-cold  bath.  But  this  (as  well  as  rubbing  with  alcohol)  is  a 
shock  to  the  nervous  system,  and  it  drives  the  blood  inward  and  checks  instead 
of  starting  the  sweat  glands.  It  should  be  used  only  when  a  physician  advises  it, 
or  when  the  fever  runs  so  high  that  it  must  be  quickly  lowered.  Sponging  with 
warm  or  tepid  water  is  safer,  and  is  often  sufficient. 


2OO  HUMAN  PHYSIOLOGY 


BATHING 

Dead  epidermal  cells  of  the  skin  and  oil  from  the  seba- 
ceous glands  become  mixed  with  perspiration  and  dust  and 
form  a  considerable  amount 1  of  waste  matter  on  the  skin. 
This  should  be  removed,  or  it  will  form  a  breeding  place  for 
many  germs,  which  may  get  down  into  the  hair  follicles  and 
cause  pimples  and  other  skin  troubles.2  It  is  important, 
therefore,  to  keep  the  skin  clean,  and  to  do  this,  soap  should^ 
be  used  on  the  skin  to  dissolve  the  oily  matter.  For  purposes 
of  cleanliness,  a  moderately  warm  bath  is  best,  but  aside  from 
cleansing  the  skin,  bathing  has  little  effect  on  the  body  except 
through  the  temperature  of  the  water.  A  hot  or  cold  bath, 
however,  may  have  a  decided  effect  on  the  nervous  system, 
and  through  it,  on  the  whole  body. 

Cold  Baths.  When  a  cold  bath  is  taken,  the  blood  vessels 
of  the  skin  contract  and  send  the  blood  to  the  heart,  lungs, 
brain,  and  other  internal  parts  of  the  body.  This  quickens 
the  circulation  and  respiration,  and  causes  more  food  to  be 
oxidized  in  the  body,  thus  producing  more  body  heat.  After 
the  bath,  the  reaction  (the  return  of  the  blood  to  the  skin) 
usually  comes,  warming  and  reddening  the  skin,  and  giving 
the  bather  a  fresh  and  pleasurable  feeling.  Rubbing  the 
skin  helps  to  bring  on  the  reaction.  Sometimes  when  the 
water  is  very  cold,  or  the  person  taking  the  bath  is  weak  or 
unaccustomed  to  cold  baths,  the  reaction  does  not  follow,  and 
the  bather  is  left  weak  and  shivering.  This  is  decidedly 
injurious.  A  person  should  train  himself  gradually  to  a  cold 
bath,  and  should  always  be  sure  that  the  temperature  of  the 
water  is  not  so  low,  and  the  time  spent  in  the  bath  not  so 

1  It  has  been  estimated  that  a  pint  of  epidermal  cells  scale  off  one  arm  and 
hand  in  a  month.  2  Blackheads  are  hair  follicles  that  have  become  stopped  up. 


THE  SKIN"  AND    THE  BODY  HEAT  2OI 

long,  that  the  reaction  will  not  come  promptly.  Some  indi- 
viduals do  not  seem  able  to  accustom  themselves  to  cold  baths 
without  too  great  a  shock  to  the  nervous  system,  and  these 
persons  should  bathe  only  in  warm  or  tepid  water. 

Warm  Baths.  Most  of  the  effects  of  a  hot  bath  are  exactly 
opposite  to  the  effects  of  a  cold  bath.  A  hot  bath  opens  the 
vessels  in  the  skin,  and  draws  the  blood  to  the  surface  of  the 
body  and  away  from  the  muscles  and  the  internal  organs. 

Time  for  bathing.^Since  a  cold  bath  sends  the  blood  to 
the  brain  and  causes  a  greater  amount  of  food  to  be  oxidized 
in  the  body,  the  best  time  to  take  such  a  bath  is  in  the  morn- 
ing, when  we  wish  to  have  our  energies  aroused  and  to  wake 
up  for  the  work  of  the  day.  It  should  not  be  taken  when  one 
is  very  hot  or  tired.  The  best  time  for  a  warm  bath  is  just 
before  bedtime,  after  the  work  of  the  day  is  done.  Persons 
who  are  troubled  with  insomnia  (sleeplessness)  sometimes 
find  that  a  warm  bath  enables  them  to  go  to  sleep.  One  who 
has  been  engaged  in  very  hard  exercise  will  find  that  a  hot 
bath  draws  the  blood  away  from  the  muscles  to  the  skin. 
A  warm  bath  should  not  be  taken  immediately  before  or 
after  eating,  because  it  draws  the  blood  from  the  digestive 
organs.  Tepid  baths  have  no  particular  effect  on  the  body, 
and  may  be  taken  at  any  time.  Unless  the  water  is  cold,  a 
swim,  like  other  exercise,  may  be  taken  at  almost  any  time 
except  just  before  and  for  a  time  after  eating.1 

1  It  is  well  to  know  that  "  cramps,"  with  which  swimmers  are  occasionally 
seized,  is  believed  to  come  on  more  frequently  after  eating.  Just  what  the  trouble 
is  in  cramps  is  not  well  understood.  One  theory  is  that  when  the  diaphragm  is 
hindered  in  its  downward  movement  by  a  full  stomach,  the  severe  exercise  of 
swimming  and  the  force  required  to  push  out  the  body  walls  in  the  water,  throws 
so  heavy  a  task  on  the  respiratory  muscles  that  these  muscles  suddenly  fail  in 
their  work  and  the  breathing  stops.  Whether  or  not  this  theory  is  correct,  it  is 
probably  best  to  follow  the  old  rule  of  not  taking  a  swim  for  two  hours  after  eating. 


202  HUMAN  PHYSIOLOGY 

THE   HEATING   OF  BUILDINGS 

The  lower  animals  depend  on  the  food  which  they  burn  in 
their  bodies  to  keep  up  their  heat,  but  man  has  learned  the 
use  of  fire,  and  in  the  colder  portions  of  the  earth  heats  his 
houses.  This  has  many  advantages,  but  it  has  certain  dis- 
advantages ;  for  when  we  pass  from  a  warm  house  into  cold 
winter  air,  there  is  suddenly  a  very  great  change  in  the 
amount  of  heat  that  is  lost  from  the  body. 

Overheated  Rooms.  Many  rooms  both  in  private  dwell- 
ings and  in  schoolhouses  and  other  public  buildings  are  kept 
too  hot.  This  is  injurious  for  the  following  reason: 

In  a  warm  room  the  skin  is  moistened  with  perspiration 
and  the  blood  is  drawn  to  the  surface  of  the  body.  When  a 
person  passes  from  a  warm  room  to  the  cold  outside  air,  the 
perspiration  on  the  skin  continues  to  evaporate  and  take  heat 
out  of  the  body,  and  large  amounts  of  heat  are  lost  before 
the  blood  can  be  cut  off  from  the  skin.  An  overheated 
room  is  injurious  because  on  leaving  it  too  mucJi  Jieat  is  lost 
from  the  body,  and  the  body  is  chilled.  Sitting  down  to  rest 
in  the  cold  outside  air  when  one  is  hot  from  exercising  may 
in  the  same  way  cause  the  body  to  be  chilled. 

Underheated  Rooms.  Cold  rooms  are  injurious  because  in  them 
the  body  loses  too  much  heat  and  becomes  cold  and  chilled.  Cold 
floors  are  common,  and  little  children,  especially,  suffer  from 
them.  The  temperature  of  the  air  at  the  floor  of  a  room  is  often 
20  degrees  lower  than  the  temperature  of  the  air  a  few  feet 
above  the  floor.  When  small  children  get  down  to  play  on  the 
floor  they  may  be  passing  from  a  warm  to  a  cold  atmosphere,  and 
they  often  suffer  from  cold  in  a  room  that  in  some  parts  is  suffi- 
ciently heated.  Fires  should  be  built  on  cold  days  in  the  spring 
and  fall,  or  colds  will  follow  staying  in  rooms  that  are  too  cool. 


THE  SKIN  AND   THE  BODY  HEAT  203 

How  chilling  the  Body  injures  it.  The  most  common 
result  of  chilling  the  body  is  a  cold.  It  is  practically  certain 
that  a  cold  is  a  germ  disease,  and  it  is  thought  that  allow- 
ing the  body  to  become  too  cold  weakens  it,  so  that  the 
germs  can  grow  in  it  and  cause  the  cold.  One  great  ad- 
vantage that  is  claimed  for  cold  baths  is  that  by  training 
the  vessels  of  the  skin  to  close  quickly  they  prevent  the 
body  from  becoming  chilled  and  give  those  who  take  them 
marked  freedom  from  colds. 

The  Use  of  the  Thermometer.  About  70  degrees  is  the 
proper  temperature  for  a  room  in  which  people  are  sitting. 
In  keeping  a  room  at  the  proper  temperature,  a  thermometer 
is  a  very  great  aid.  The  temperature  of  different  parts  of 
the  room  should  be  tested  and  some  method  of  heating  used 
that  will  warm  all  parts  of  the  room  as  evenly  as  possible,  so 
that  some  of  the  people  in  the  room,  will  not  be  too  hot  while 
others  are  too  cold,  or  one  part  of  the  body  be  warm  while 
another  part  of  it  is  cold.  Some  persons  prefer  rooms  heated 
to  75  or  80  degrees,  and  if  a  schoolroom  is  not  provided  with 
a  thermometer,  there  is  great  danger  that  the  whole  roomful 
of  children  will  be  kept  too  warm.  Where  rooms  are  heated 
with  stoves,  it  will  be  found  that  a  large  stove  gives  a  more 
steady,  even  heat  than  a  small  stove  gives.  Having  one  part 
of  the  body  hot  and  another  part  cold  is  decidedly  injurious, 
so  cold  floors  and  cold  drafts  are  to  be  avoided  wherever 
possible. 

CLOTHING 

Birds  have  feathers  and  most  mammals  have  a  coat  of  hair 
to  retain  the  body  heat,  but  in  man  the  hair  on  the  body  is  so 
fine  and  thin  that  it  is  of  little  use  as  a  protection  from  the 
cold.  In  the  colder  regions  of  the  earth,  man  has,  therefore, 


204  HUMAN  PHYSIOLOGY 

been  compelled  to  clothe  himself  to  keep  up  his  body  heat. 
The  chief  physio  logical- use  of  clothing  is  to  retain  the  body  heat. 
Clothing  also  saves  the  body  from  wounds  and  bruises  and 
protects  it  from  the  heat  and  light  of  the  sun. 

How  Clothing  retains  the  Body  Heat.  Heat  passes  with 
great  difficulty  through  dry  air,  and  clothing  prevents  the 
escape  of  the  body  heat  chiefly  through  holding  air  in  the 
little  crevices  in  the  cloth.  The  fur  of  animals  forms  a  very 
warm  body  covering,  and  in  a  number  of  animals  (including 
the  cat,  rabbit,  and  sheep)  it  has  been  found  that  on  an  average 
about  2  per  cent  of  the  fur  is  hair,  and  98  per  cent  of  it  is 
air  that  is  held  in  the  little  spaces  between  the  hairs. 

The  Best  Materials  for  Clothing.  Woolen  clothing  is 
warmer  than  cotton  or  linen.  Wool  is  therefore  the  best 
material  for  winter  clothing,  but  in  hot  summer  weather,  cot- 
ton and  linen  clothing  may  be  superior  to  woolen.  Woolen 
clothing  is  warmer  than  the  others  because  it  has  many  little 
air  spaces  between  the  threads ;  in  cotton  and  linen  cloth 
the  threads  are  harder,  and  are  woven  more  solidly  together, 
so  that  a  smaller  amount  of  air  is  held  in  the  cloth. 

Wool  is  superior  to  cotton  and  linen  for  winter  clothing  for 
another  reason,  also.  It  will  absorb  more  water  than  either 
of  the  others,  and  therefore  does  not  become  dampened  so 
quickly  by  the  perspiration.  Cold  water  or  cold,  wet  clothing 
touching  the  skin  takes  the  heat  out  of  the  body  with  great 
rapidity,  and  if  a  person  clothed  in  cotton  or  linen  exercises 
until  he  perspires,  his  clothing  becomes  damp ;  then  if  he 
rests  in  a  cold  atmosphere  the  heat  may  escape  too  rapidly 
from  the  body,  and  a  cold  follow. 

Tight-fitting  and  Insufficient  Clothing.  Tight  clothing,  by 
interfering  with  the  circulation  of  the  blood,  may  cause  cold- 
ness in  some  parts  of  the  body.  Cold  feet  are  often  caused 


THE  SKIN  AND    THE  BODY  HEAT  2O$ 

by  tight  shoes,  or  by  tight  clothing  around  the  legs  that  pre- 
vents the  descent  of  the  warm  blood  to  the  feet.  Insufficient 
clothing  on  the  legs  also  causes  cold  feet,  because  cold  on  the 
legs  causes  the  arteries  in  them  to  contract,  and  lessens  the 
amount  of  blood  that  is  supplied  to  the  feet.  Many  children 
surfer  from  being  dressed  in  stockings  so  short  that  they  leave 
a  portion  of  the  leg  uncovered.  It  is  important  not  only  that 
sufficient  clothing  be  worn  but  that  the  clothing  be  so  distrib- 
uted on  the  body,  that  all  parts  of  the  body  will  be  kept  warm. 

Other  Hygienic  Points  connected  with  Clothing.  Wet  cloth- 
ing takes  the  heat  out  of  the  body  and  is  especially  likely  to 
cause  colds.  Damp  feet  are  a  common  cause  of  sickness,  and 
when  rubbers  are  needed  to  keep  the  feet  dry  they  should 
always  be  worn. 

Wearing  heavy  clothing  indoors  has  the  same  effect  as 
staying  in  an  overheated  room.  An  overcoat  should  not 
be  worn  in  the  house,  but  should  be  put  on  before  going  out- 
doors, to  protect  the  body  from  the  sudden  change  to  the  cold 
of  the  outside  air. 

Heavy  clothing  should  be  worn  in  the  spring  and  fall  when 
the  weather  demands  it.  If  in  the  spring  the  weather  turns 
cool  after  heavy  clothing  has  been  taken  off,  the  heavy  cloth- 
ing should  be  put  on  again.  The  clothing  and  the  heating 
of  buildings  should  be  adapted  to  the  weather,  and  if  thin 
clothing  is  worn  and  fires  are  allowed  to  go  out  on  cold 
days  in  the  spring  and  fall,  colds  and  sickness  will  follow. 

Summary.  The  skin  forms  a  protective  covering  for  the 
body,  is  an  organ  of  feeling,  regulates  the  body  heat,  and 
excretes  water.  The  outer  layer  of  the  skin  is  called  the 
epidermis.  The  dermis  is  a  layer  of  connective  tissue  under 
the  epidermis,  and  the  subcutaneous  layer  lies  below  the 
dermis.  Fat  is  stored  in  this  layer. 


206  HUMAN  PHYSIOLOGY 

The  sweat  glands  take  water  from  the  blood  and  pour  it 
out  on  the  skin  as  perspiration.  By  the  evaporation  of  the 
perspiration  the  body  is  cooled.  The  sweat  glands  are  under 
the  control  of  the  nervous  system. 

A  hair  grows  in  a  hair  follicle  and  rests  on  a  hair  papilla. 
It  grows  from  the  epidermal  cells  at  its  base.  The  sebaceous 
glands  secrete  a  clear  oil  for  the  hair.  Brushing  arid  a  clean 
scalp  are  beneficial  to  the  hair.  Dandruff  is  in  all  probability 
a  germ  disease  and  may  be  contracted  from  brushes  and 
combs  that  other  persons  have  used.  Baldness  is  usually  due 
to  dandruff  or  tight  hats. 

The  nails  grow  from  the  epidermis.  They  protect  the 
fingers  and  are  useful  in  picking  up  small  objects. 

The  temperature  of  the  healthy  human  body  is  always  near 
98|  degrees.  The  skin  regulates  the  escape  of  heat  from  the 
body  by  controlling  the  amount  of  blood  that  comes  to  the 
skin  and  by  the  action  of  the  sweat  glands.  The  amount 
of  heat  produced  in  the  body  is  regulated  by  the  amount  of 
food  that  is  oxidized,  extra  food  being  burned  when  the  body 
is  cold. 

In  sickness  the  temperature  of  the  body  may  rise  too  high 
or  fall  too  low.  The  chief  trouble  in  fever  is  that  not  enough 
heat  is  lost,  the  sweat  glands  usually  failing  to  work.  In  a 
chill  the  blood  is  cut  off  from  the  skin. 

The  skin  should  be  kept  clean  so  that  germs  will  not  find 
food  on  it. 

A  cold  bath  is  best  taken  in  the  morning  and  a  warm  bath 
at  bedtime.  Cold  baths  are  injurious  when  they  are  not 
promptly  followed  by  the  reaction. 

Overheated  rooms  cause  the  body  to  be  chilled  after  leav- 
ing them ;  underheated  rooms  cause  the  body  to  be  chilled 
while  in  them ;  and  chilling  of  the  body  is  followed  by  colds. 


THE  SKIN  AND   THE  BODY  HEAT  207 

A  thermometer  should  be  used  to  determine  whether  rooms 
have  the  proper  temperature.  ' 

Clothing  retains  the  heat  by  holding  air  in  its  pores. 
Wool  is  a  warmer  material  for  clothing  than  cotton  or  linen. 
Tight-fitting  clothing  causes  coldness  of  parts  of  the  body  by 
interfering  with  the  circulation.  Wet  clothing,  wearing  heavy 
clothing  indoors,  and  insufficient  clothing  during  cold  weather 
in  the  spring  and  fall  are  causes  of  sickness. 


QUESTIONS 

Give  the  four  functions  of  the  skin.  Name  the  layers  of  the  skin. 
What  is  a  corn?  What  gives  the  color  to  the  skin?  What  is  a 
freckle? 

Of  what  is  the  dermis  composed?  What  is  a  papilla?  Where 
is  the  subcutaneous  layer?  Of  what  is  it  composed,  and  what  is 
deposited  in  it? 

What  are  the  pores  in  the  skin  ?  Describe  a  sweat  gland.  What 
is  the  function  of  the  sweat  glands?  Where  does  the  water  of  the 
perspiration  come  from  ?  Why  do  we  not  see  the  perspiration  on 
the  skin  at  all  times?  How  does  perspiration  cool  the  skin?  What 
controls  the  sweat  glands  ? 

What  is  a  hair  follicle?  a  hair  papilla?  With  what  is  the  follicle 
lined  and  the  papilla  covered?  When  the  hair  grows,  where  do  the 
cells  multiply?  From  what  layer  of  the  skin  is  the  hair  formed ?  How 
does  a  hair  get  food  ?  Where  are  the  sebaceous  glands  ?  What  is 
their  function  ?  What  causes  the  hair  to  stand  on  end  ? 

Give  two  reasons  why  brushing  benefits  the  hair.  What  is  the 
cause  of  dandruff?  How  may  this  disease  be  contracted  ?  What 
causes  baldness  ? 

From  what  layer  of  the  skin  are  the  nails  formed?  What  causes 
their  pink  color?  What  causes  the  white  spot  at  the  base  of  a  nail? 
What  is  the  function  of  the  nails  ? 


208  HUMAN  PHYSIOLOGY 

What  is  the  temperature  of  the  body  in  health  ?  Give  two  ways  by 
which  the  body  heat  is  regulated.  In  what  two  ways  does  the  skin 
regulate  the  escape  of  the  heat  from  the  body  ?  How  do  the  cells 
regulate  the  amount  of  heat  produced?  Why  must  persons  living 
outdoors  have  more  heat  than  those  who  live  indoors? 

What  is  fever?     What  is  its  cause ?     What  causes  a  chill? 

Why  should  the  skin  be  kept  clean?  Give  the  effect  of  a  cold 
bath  on  the  blood  vessels  of  the  skin.  Give  some  other  effects  of 
a  cold  bath.  When  is  a  cold  bath  injurious? 

Give  the  effect  of  a  warm  bath  on  the  vessels  of  the  skin  ;  on  the 
distribution  of  the  blood.  When  should  a  cold  bath  be  taken?  a 
warm  bath?  Why  is  a  warm  bath  harmful  immediately  before  or 
after  eating?  What  is  the  effect  of  a  tepid  bath?  Why  should  one 
not  take  a  swim  immediately  after  eating? 

Why  are  overheated  rooms  injurious?  underheated  rooms?  How 
does  chilling  the  body  injure  it?  How  do  cold  baths  prevent  this? 
What  is  the  proper  temperature  for  a  living  room?  Why  is  the  use 
of  the  thermometer  important? 

What  is  the  chief  physiological  use  of  clothing  ?  How  does  clothing 
retain  the  body  heat?  Which  is  the  warmest  ma-terial  for  clothing? 
Why?  Which  material  absorbs  moisture  best?  What  is  the  effect  of 
tight  clothing  on  the  heat  of  the  body?  Why  should  the  feet  be  kept 
dry?  What  is  the  effect  of  wearing  heavy  clothing  indoors?  At  what 
time  of  the  year  should  especial  care  be  taken  to  wear  sufficient 
clothing? 


THE  SKIN  AND   THE  BODY  HEAT  209 


REVIEW    QUESTIONS 

Chapter  XL  Why  is  the  circulation  of  the  blood  necessary? 
Trace  the  blood  from  right  auricle  to  right  auricle.  What  does  the 
blood  lose  and  gain  in  the  capillaries  of  the  body?  of  the  lungs? 
How  is  the  oxygen  carried  in  the  blood?  What  is  lymph?  How  is 
it  returned  to  the  blood?  What  is  the  function  of  a  lymph  node? 
Mention  some  common  causes  of  injury  to  the  heart. 

Define  :  auricle  \  ventricle  ;  artery ;  vein ;  capillary ;  hemoglobin  ; 
plasma ;  thoracic  duct. 

Chapter  XII.  What  is  the  object  of  respiration?  Why  is  oxygen 
necessary  to  the  body?  Why  must  the 'body  get  rid  of  its  carbon 
dioxid?  What  does  the  air  gain  and  lose  in  the  lungs?  Why  does 
mouth  breathing  cause  disease?  Name  five  points  connected  with 
the  hygiene  of  the  respiratory  organs.  What  kind  of  diseases  chiefly 
affect  these  organs  ?  How  is  voice  produced  ?  How  are  the  vocal 
cords  thrown  into  and  out  of  action? 

Define  :  pleura ;  diaphragm  ;  uvula  ;  larynx  ;  epiglottis  ;  bronchial 
tubes  ;  mucus  ;  cilia ;  thyroid  ;  cricoid  ;  arytenoid. 

Chapter  XIII.  Why  is  ventilation  necessary?  How- much  fresh 
air  does  a  person  need  in  an  hour?  How  much  air  space  for  each 
person  should  there  be  in  a  public  building?  in  a  private  house? 
Explain  how  a  fireplace  or  stove  ventilates  a  room.  Why  is  the  ven- 
tilation of  sleeping  rooms  especially  important? 

Chapter  XIV.  What  is  the  usual  cause  of  illness?  How  are  the 
poisons  that  are  in  the  body  produced  ?  What  is  the  function  of  the 
kidneys?  Explain  how  the  wastes  get  from  the  blood  into  the 
ureters.  What  diseases  of  the  kidneys  are  caused  by  alcohol  ? 

Define  :  uric  acid  ;  renal  corpuscle. 

Chapter  XV.  Give  four  functions  of  the  skin.  Explain  how  the 
perspiration  gets  from  the  blood  to  the  surface  of  the  skin.  Draw  a 
diagram  of  a  hair  in  its  follicle.  What  is  the  temperature  of  the 
human  body  ?  How  is  the  escape  of  the  heat  from  the  body  con- 
trolled? When  is  a  cold  bath  injurious?  What  is  the  danger  from 
an  overheated  room?  from  a  cold  room?  Mention  some  hygienic 
points  connected  with  clothing. 

Define  :  epidermis  ;  dermis  ;  papilla ;  follicle  ;  sebaceous. 


CHAPTER   XVI 

THE  NERVOUS   SYSTEM 

THE  first  great  work  of  the  nervous  system  is  to  cause  all 
the  parts  of  the  body  to'  work  harmoniously  together.  The 
second  is  to  act  as  the  organ  of  the  mind.1  In  a  former  chap- 
ter we  learned  something  of  the  way  the  body  is  ruled,  and 
we  have  seen  in  a  general  way  how  the  different  organs  are 
controlled  and  kept  at  work.  In  this  chapter  we  shall  take 
up  in  more  detail  the  structure  and  the  function  of  the  ner- 
vous system. 

Nerve  Cells  and  Nerve  Fibers.  Nerve  tissue  contains  nerve 
cells  and  nerve  fibers.  The  nerve  cells  are  much  branched, 
are  larger  than  most  of  the  body  cells,  and  have  a  gray  color. 
Most  of  them  are  found  in  the  brain2  and  spinal  cord,  but 
small  groups  of  nerve  cells  called  ganglia  3  (singular,  gang- 
lion) are  found  in  various  parts  of  the  body. 

1 A  simple  and  easy  way  of  treating  of  the  relation  between  the  brain  and  the 
mind  is  to  say  that  the  mind  is  in  the  brain,  and  that  it  is  the  cells  of  the  brain 
that  think  and  feel.  It  may  be  objected,  however,  that  we  do  not  know  where 
the  mind  is  ;  that  it  can  exist  apart  from  the  body  altogether  ;  and  that  while  the 
function  of  the  muscle  cells  is  to  contract,  and  the  function  of  gland  cells  is  to 
secrete,  it  is  perhaps  not  allowable  to  say  that  the  function  of  the  brain  cells  is  to 
think.  The  brain,  however,  is  in  some  way  closely  associated  with  the  mind,  and 
we  have  therefore  spoken  of  it  as  the  organ  of  the  mind. 

2  It  is  estimated  that  there  are  over  9,000,000,000  nerve  cells  in  the  cerebrum 
alone. 

3 There  is  a  ganglion  on  the  root  of  each  spinal  nerve  (Fig.  103),  but  most  of 
the  ganglia  belong  to  the  sympathetic  system  (Fig.  106).  They  are  found  chiefly 

210 


THE  NERVOUS  SYSTEM 


211 


A  nerve  fiber  contains  a  gray  central  axis  cylinder,  which 
is  a  branch  of   the  cytoplasm  of  a  f 

nerve  cell.  A  nerve  fiber  is  there- 
fore always  connected  with  a  nerve 
cell  and  may  almost  be  considered 
as  a  branch  of  a  cell.  A  nerve  cell 
and  nerve  fiber  taken  together  are 
called  a  neuron.  The  nerve  mes- 
sages, which  are  also  called  stimuli 
and  nerve  imptilses,  travel  through 
a  fiber  in  the  gray  central  axis 
cylinder. 

Efferent  and  Afferent  Nerve 
Fibers.1  The  nerve  fibers  in  which 
the  impulses  travel  from  the  brain 
and  cord  are  called  efferent  fibers. 
They  take  messages  to  the  muscles 
which  cause  the  muscles  to  contract, 
and  to  all  the  glands  and  organs 
of  the  body,  causing  each  to  work. 
The  fibers  which  carry  impulses 
from  the  different  parts  of  the 
body  to  the  brain  and  cord  are 
called  afferent  fibers. 

The  Nervous  System  as  a  Con- 
nector of  the  Body  Parts.  As  you 

in  the  internal  parts  of  the  body,  and  are  not 
found  in  the  limbs,  or  to  any  extent  among  the 
voluntary  muscles.  Many  of  them  are  micro- 
scopic. 

1  Efferent  and  afferent  nerve  fibers  are  often 
called  motor  and  sensory  fibers.  FIG.  97.  A  neuron. 


212 


HUMAN  PHYSIOLOGY 


will  understand  better  after  studying  reflex  actions,  a  great 
portion  of  the  work  of  the  nervous  system  in  governing  the 
body  is  done  by  putting  the  different  body  parts  into  com- 
munication with  each  other.  In  a  former  chapter  (page  23) 
we  have  spoken  of  the  nervous  system  as  the  ruler  of  the 
body.  In  reality,  it  resembles  a  telephone  system  as  much 


FlG.  98.  A  shows  the  number  of  wires  necessary  to  connect  twelve  houses  by  tele- 
phone without  a  central  office.  B  shows  the  number  of  wires  necessary  to  connect  the 
same  number  of  houses  through  a  central  office.  The  number  of  nerve  fibers  that 
would  be  necessary  to  connect  all  parts  of  the  body  without  a  brain  and  spinal  cord 
to  act  as  a  central  office  can  hardly  be  imagined. 

as  it  does  a  monarch.  As  on  a  telephone  system  the  dif- 
ferent houses  are  put  into  connection  with  each  other 
through  a  central  office,  so  the  different  parts  of  the  body 
are  connected  through  the  brain  and  spinal  cord.  In  many 
parts  of  the  body  each  cell  is  supplied  with  a  nerve  fiber 
(Fig.  102)  and  the  body  has  in  it  a  perplexing  network  of 
nerves.  By  examining  Figure  98,  you  can  understand  what 
a  hopeless  tangle  the  nervous  system  would  become  if  an 
attempt  were  made  to  connect  all  the  cells  of  the  body  with- 
out a  brain  and  spinal  cord  to  act  as  a  central  office. 


THE  NERVOUS  SYSTEM  213 


THE  CENTRAL  NERVOUS   SYSTEM 

The  central  nervous  system  consists  of  the  brain,  the  spinal 
cord,  and  the  nerves  arising  from  the  brain  and  cord.  Twelve 
pairs  of  nerves  pass  out  from  the  brain,  and  thirty-one  pairs 
from  the  cord,  putting  these  nerve  centers  in  connection  with 
all  the  body  parts. 

The  Brain.  The  spinal  cord  is  only  a  little  thicker  than  a 
lead  pencil.  The  brain  fills  the  whole  cranial  cavity.  The 


MEDULLA -OBLONGATA 

FIG.  99.     Longitudinal  section  of  the  brain. 

cord  weighs  about  one  and  one  half  ounces  and  the  brain 
weighs  about  fifty  ounces.  The  brain,  therefore,  composes 
by  far  the  greatest  part  of  the  central  nervous  system.  Its 
three  main  divisions  are  the  cerebrum,  the  cerebellum,  and 
the  medulla  oblongata. 

The  Cerebrum.     The  cerebrum  comprises  more  than  three 
fourths  of  the  entire  brain.     It  is  divided  by  a  deep  groove  in 


214 


HUMAN  PHYSIOLOGY 


its  upper  surface  into  a  right  and  a  left  hemisphere.  The  sur- 
face of  the  cerebrum  is  thrown  into  a  great  number  of  folds 
and  wrinkles  called  convolutions  (Fig.  13). 

A  layer  on  the  surface  of  the  cerebrum  is  composed  of 
nerve  cells,  and  therefore  has  a  gray  color.  This  is  the  gray 
matter  of  the  brain,  with  which  the  mind  is  associated.  The 
inner  and  lower  parts  of  the  cerebrum  are  chiefly  composed 
of  nerve  fibers. 

The  Fibers  of  the  Cerebrum.  A  great  network  of  fibers 
connects  all  the  different  parts  of  the  cerebrum  with 

each  other.  Other  fibers  connect 
the  cerebrum  and  the  cerebellum, 
and  countless  fibers  run  through  the 
medulla  into  the  spinal  cord,  and 
connect  the  cerebrum  with  the  body 
parts  below.  In  the  medulla  most 
of  the  fibers  from  the  cerebrum  cross 
so  that  the  right  hemisphere  of  the 
cerebrum  is  connected  with  the  left 
side  of  the  body,  and  the  left  hemi- 
sphere is  connected  with  the  right 
side  of  the  body.  If,  because  of 
injury  or  of  apoplexy,  a  blood  clot 
forms  on  the  right  side  of  the  cere- 
be  the  left  side  of  the  body  that  will  be 


FIG.  ioo.  The  cerebrum 
from  above,  showing  the  hemi- 
spheres. 


The  cerebrum  has  three  func- 


brum,    it   will 
paralyzed. 

Functions  of  the  Cerebrum. 

tions : 

The  cerebrum  is  the  seat  of  the  mind.  When  the  cerebrum 
of  a  pigeon  or  of  a  dog  is  removed,  life  may  go  on,  but  all 
memory  and  reason  are  lost,  and  the  animal  is  hopelessly 
idiotic.  Removing  the  gray  matter  on  the  surface  of  the 


THE  NER  VOUS  'SYSTEM  2 1 5 

cerebrum  has  the  same  effect  on  the  intelligence  as  re- 
moving the  whole  cerebrum. 

The  cerebrum  is  tJie  seat  of  tJie  sensations.  Nerve  messages 
from  all  parts  of  the  body  come  into  the  cerebrum  and 
cause  the  sensations  of  light,  sound,  taste,  smell,  touch,  heat, 
cold,  hunger,  fatigue,  and  other  sensations.  Without  a 
cerebrum  an  animal  has  no  mind,  and  without  a  mind  there 
could,  of  course,  be  no  knowledge  of  the  afferent  nerve 
impulses  and  no  such  thing  as  a  sensation  of  pain,  cold, 
hunger,  or  any  other  kind  of  sensation. 

The  cerebrum  originates  and  sends  out  impulses  that  cause 
voluntary  movements.  When  we  decide  to  move,  the  cere- 
brum can  start  out  impulses  which  cause  the  muscles  to  con- 
tract. We  have,  therefore,  the  power  of  voluntary  movement 
— the  power  to  make  the  muscles  work  when  we  wish  them 
to  do  so. 

The  Cerebellum.  The  cerebellum  lies  behind  and  above 
the  medulla,  and  is  covered  over  by  the  back  lobes  of  the 
cerebrum.  Many  nerve  fibers  connect  the  two  sides  of  the 
cerebellum  with  each  other.  The  cerebellum  is  also  con- 
nected with  the  cerebrum,  and  through  the  medulla  and  cord 
with  most  of  the  body.  The  cells  in  the  cerebellum  are 
mainly  in  a  layer  on  the  surface,  and  the  fibers  in  its  central 
lobe  are  arranged  so  that  they  form  a  tree-like  mass  of  white 
matter,  called  the  arbor  vita  ("tree  of  life  "). 

Function  of  the  Cerebellum.  There  is  much  dispute  about  the 
function  of  the  cerebellum,  but  it  seems  to  be  about  as  follows  : 

The  cerebellum  causes  all  the  muscles  to  keep  a  proper 
amount  of  contraction.  When  the  cerebellum  is  injured,  all 
the  muscles  are  relaxed,  instead  of  keeping  a  certain  amount 
of  contraction  as  they  usually  do.  The  result  is  trouble  in 
the  movements,  because  when  the  cerebrum  causes  a  muscle 


2l6  HUM  A  ft  PHYSIOLOGY 

to  contract,  the  antagonistic  muscle  does  not  work  in  opposi- 
tion and  steady  the  motion.  This  causes  jerky  movements 
and  movements  that  often  go  too  far  (page  67). 

The  second  function  of  the  cerebellum  is  to  assist  in  coor- 
dinating the  movements  of  the  muscles  of  locomotion.  When 
a  man's  cerebellum  is  injured,  he  staggers  about  as  though 
he  were  intoxicated.  His  muscles  are  not  paralyzed,  but 
some  of  them  contract  too  powerfully,  some  not  powerfully 
enough,  and  often  they  fail  to  contract  at  the  right  moment. 
The  cerebellum  seems  to  cause  the  muscles  that  are  used  in 
standing,  walking,  and  running  to  act  in  an  orderly  manner, 
and  thus  keeps  the  body  from  falling. 

The  Pons.  The  pons  lies  in  the  pathway  between  the  dif- 
ferent parts  of  the  brain,  and  it  is  composed  chiefly  of  fibers 
that  connect  the  cerebrum,  cerebellum,  and  medulla.  There 
are  also  in  the  pons  many  fibers  that  connect  the  two  sides  of 
the  cerebellum.  From  one  side  of  the  cerebellum  the  fibers 
pass  forward  to  the  pons,  cross  over  in  it,  and  turn  backward 
into  the  other  side  of  the  cerebellum.  The  word  "pons" 
means  a  bridge,  and  the  pons  is  a  bridge  connecting  all  parts 
of  the  brain. 

The  Medulla.  The  medulla  contains  many  nerve  fibers 
that  connect  the  higher  parts  of  the  brain  with  the  spinal 
cord  and  the  body.  The  greater  part  of  the  head  and  many 
of  the  internal  organs,  including  the  heart  and  lungs,  are  sup- 
plied by  nerves  that  rise  from  the  medulla.  When  the  cere- 
brum is  removed  from  an  animal,  the  intelligence  is  lost,  but 
life  may  go  on ;  when  the  cerebellum  is  injured,  the  control 
of  the  muscles  is  lost;  but  when  the  medulla  is  injured,  death 
comes  at  once  because  tte  breathing  stops. 

The  Function  of  the  Medulla.  The  medulla  conducts  stimuli 
to  and  from  the  higJier  parts  of  the  brain,  and  it  acts  as  a  reflex 


THE  NERVOUS  SYSTEM  2 1/ 

center  for  the  parts  of  the  body  that  receive  nerves  from  it. 
To  understand  what  is  meant  by  a  reflex  center  we  must 
know  what  a  reflex  action  is.  Before  taking  up  this  subject 
we  shall  discuss  the  spinal  cord,  for  like  the  medulla  the 
spinal  cord  is  a  reflex  center. 

The  Spinal  Cord.  The  inner  part  of  the  spinal  cord  is 
composed  of  gray  matter  (cells)  and  the  outer  part  of  white 
matter  (fibers).  All  the  skin  and  the  voluntary  muscles  of 
the  body  parts  below  the  neck  are  supplied  by  the  thirty-one 
pairs  of  spinal  nerves,  and  through  the  sympathetic  system 
the  spinal  cord  is  connected  with  the  internal  organs,  the 
sweat  glands,  and  the  blood  vessels. 

Functions  of  the  Spinal  Cord.  The  spinal  cord  has  the  same 
two  functions  as  the  medulla.  The  first  of  these  functions  is 
to  conduct  impulses  to  and  from  tJie  brain.  The  nerve  impulses 
that  come  in  through  the  spinal  nerves  pass  up  to  the  brain 
through  the  cord,  and  the  nerve  impulses  sent  out  by  the 
brain  to  the  glands  and  muscles  come  down  through  the 
cord.  For  this  reason,  if  the  spinal  cord  be  cut  across,  all 
parts  of  the  body  supplied  by  nerves  from  below  the  cut 
lose  their  feeling  and.  are  paralyzed.  The  impulses  from 
these  parts  cannot  get  up  to  the  brain  to  cause  sensations 
of  feeling,  and  the  commands  of  the  brain  cannot  get  to  the 
muscles  below  the  cut  to  cause  them  to  move.  The  other 
function  of  the  spinal  cord  is  to  act  as  a  reflex  center. 

Reflex  Actions.  Reflex  actions  are  actions  that  are  caused 
by  impulses  wJiicJi  start  in  afferent  nerves.  An  example 
will  give  the  clearest  idea  of  a  reflex. 

Suppose  you  burn  your  finger  by  touching  a  candle  flame 
(Fig.  101).  The  heat  starts  an  impulse  up  the  afferent  nerve 
fibers.  The  impulse  passes  into  the  spinal  cord,  then  into 
the  efferent  nerve,  and  traveling  down  to  the  muscles  of  the 


218 


HUMAN  PHYSIOLOGY 


arm,  causes  them  to  contract  and  jerk  the  hand  away.  An 
impulse. also  goes  on  up  to  the  brain  and  causes  a  sensation 
of  pain,  but  the  hand  is  moved  before  the  pain  is  felt. 

An  action  like  this  is  a  reflex  action.  It  differs  from  the 
action  when  you  voluntarily  move  your  hand  in  the  place  in 
which  the  nerve  impulse  starts.  In  the  voluntary  action,  the 
brain  originates  and  starts  out  the  impulse.  In  the  reflex 


AFFERENT  FIBER 


FlG.  101.  Diagram  illustrating  reflex  action.  Thje  impulse  starts  in  the  finger  and 
passes  through  the  spinal  cord  to  the  muscle  of  the  arm.  B  shows  the  way  the  con- 
nections between  the  neurons  are  made  in  the  cord. 

action,  the  impulse  starts  in  the  outer  ends  of  the  nerves,  goes 
into  the  cord,  and  comes  back  down  the  nerves  to  the  muscles. 
In  this  action  the  spinal  cord  makes  the  connection  between  tJic 
afferent  and  efferent  neurons. 

Could  a  reflex  be  carried  on  without  thought  ?  Could  the 
spinal  cord  carry  on  reflexes  without  the  brain  ?  If  nothing 
disturbed  the  outer  ends  of  the  afferent  nerves,  would  a  reflex 
center  ever  cause  movement  ?  Think  out  these  problems,  and 
you  will  read  the  next  paragraphs  more  intelligently. 


THE  NERVOUS  SYSTEM 


219 


The  Spinal  Cord  as  a  Reflex  Center.  The  spinal  cord  can 
carry  on  reflexes  in  a  wonderful  way  without  the  aid  of  the 
brain.  A  shark  with  its  head  cut  off,  swims  in  a  very  natural 
manner.  A  turtle  can  walk  about  after  it  has  lost  its  head. 
If  a  drop  of  weak  acid  or  strong  vinegar  is  put  on  the  back 
of  a  brainless  frog,  the  frog 
will  wipe  the  acid  or  vinegar 
off  with  its  foot.  If  the  foot 
that  the  frog  is  using  is  held, 
the  other  foot  will  then  be  used. 
The  spinal  cord,  without  the 
brain,  can  carry  on  reflex  ac- 
tions for  any  part  of  the  body 
that  is  supplied  by  the  spinal 
nerves. 

What  the  Spinal  Cord  does 
in  Reflexes.  The  spinal  cord 
not  only  acts  as  a  connector 
between  the  afferent  and  the 
efferent  neurons,  but  it  makes 
the  right  connections  so  that 
the  proper  muscles  will  be  FlG>  ^  efferent  nerve  ending 

moved.       It    also    arranges    and    in  the  voluntary  muscle  cells.     Through 

sets  in  order  the  impulses  that  the  nerve  fibers  imPulses  come  into  the 

muscle  cells  and  cause  them  to  contract. 

come  to  it,  hurrying  them  on  to 

some  muscles,  holding  them  back  from  others,  making  some  of 
the  stimuli  strong  and  others  weak,  so  that  in  a  movement  like 
the  swimming  of  the  shark,  which  involves  almost  the  whole 
body,  each  muscle  gets  its  stimulus  so  that  it  will  contract  at 
exactly  the  right  moment  and  with  the  proper  force.  Yet 
the  spinal  cord  has  no  intelligence ;  for  a  brainless  frog  will 
sit  and  dry  up  beside  the  water  that  would  save  its  life,  and 


220  HUMAN  PHYSIOLOGY 

all  memory  is  gone  from  an  animal  that  has  only  a  spinal 
cord. 

Other  Reflex  Actions.  Reflex  centers  are  found  not  only 
in  the  cord  but  also  in  the  medulla  and  in  the  lower  part  of 
the  brain  in  front  of  the  medulla,  and  to  a  large  extent  the 
body  is  governed  through  its  reflex  centers.  If  the  eye  is 
touched,  the  eyelids  will  close.  Tickling  the  inside  of  the 
nose  causes  sneezing,  and  tickling  the  inside  of  the  larynx 
causes  coughing.  Cold  water  thrown  on  the  face  causes  the 
breath  to  be  drawn  in  suddenly,  while  a  sharp  odor,  as  of 
ammonia,  stops  the  inspiration.  Water  starting  into  the  nose 
also  checks  the  breath,  and  in  diving  birds,  water  poured 
across  the  nostrils  will  for  a  long  time  hinder  inspiration. 
Heat  on  the  skin  makes  the  vessels  relax,  and  cold  causes 
them  to  contract.  The  passing  of  digested  food  into  the 
intestine  causes  the  pancreas  to  secrete  its  juice  and  the  gall 
bladder  to  be  emptied.  Almost  the  entire  government  of 
the  internal  organs  is  carried  on  by  reflexes  of  which  we  are 
not  even  conscious,  but  when  one  of  these  organs  gets  into 
trouble,  the  impulses  that  the  afferent  nerves  carry  up  to  the 
brain  give  us  the  sensation  of  pain  and  let  us  know  that  some 
of  our  organs  need  attention. 

The  Body  Self-governing  through  the  Reflexes.  A  close 
study  of  the  reflexes  shows  that  they  are  all  purposeful. 
Even  those  which  are  carried  out  without  intelligence  or  con- 
sciousness are  all  beneficial  to  the  body.  In  studying  them, 
one  also  becomes  impressed  with  the  fact  that  the  body  itself 
brings  these  reflexes  about,  and  through  them  largely  regu- 
lates itself.  For  example,  when  the  heart  beats  hard  and  the 
arteries  are  tightly  stretched  with  blood,  it  takes  a  forcible 
contraction  to  squeeze  the  blood  out  of 'the  ventricles  into  the 
arteries.  The  pressure  of  the  blood  within  the  heart  then 


THE  NERVOUS  SYSTEM  221 

starts  impulses  up  the  afferent  nerves  of  the  lining  of  the 
heart.  These  pass  to  the  medulla,  and  impulses  which  slow 
up  the  beat  of  the  heart  come  down  the  efferent  nerves. 
Thus  the  heart  largely  regulates  itself,  the  high  blood  pres- 
sure causing  it  to  slow  its  beat.  By  the  effects  of  heat  and 
cold  on  the  skin,  the  blood  vessels  are  largely  controlled,  and 
many  other  parts  of  the  body  are  also,  to  a  certain  extent,  self- 
governing.  We  must  not  give  too  much  credit  to  the  nervous 
system  for  its  wonderful  wisdom  in  regulating  the  body,  for 
usually  the  impulses  which  cause  the  action  of  the  muscles 
and  glands  are  not  started  by  the  nervous  system  at  all,  but 
by  some  other  part  of  the  body,  and  all  that  the  nervous  sys- 
tem does  is  to  make  the  proper  connections  between  the 
afferent  and  efferent  nerves. 

Acquired  Reflexes.  Besides  these  natural  reflexes,  there 
is  another  set  of  reflexes  that  is  acquired  by  practice.  In 
skating,  riding  a  bicycle,  rowing,  boxing,  fencing,  playing  a 
piano,  and  in  almost  any  kind  of  activity,  movements  are 
made  without  thought.  The  eye  of  the  piano  player  sees  a 
certain  note,  and  his  finger  strikes  the  right  key.  The  bicycle 
rider  feels  a  slight  leaning  of  his  wheel  to  the  side,  and  he 
shifts  his  body  so  as  to  keep  the  balance.  These  movements 
have  been  made  so  often  that  they  become  reflex,  and  are 
carried  out  without  thought.1 

Habit.  The  performance  of  any  act  with  which  the  mind 
is  connected  makes  easier  a  further  performance  of  that  act. 
For  instance,  the  fingers  of  the  pianist  move  slowly  and  awk- 
wardly at  first,  since  the  mind  requires  time  to  decide  where 

1  The  acquired  reflexes  are  all  associated  with  the  mind,  and  their  seat  is  in 
the  outer  layer  of  the  cerebrum.  When  this  is  removed,  all  the  acquired  reflexes 
are  lost,  while  the  natural  reflexes  that  are  carried  on  by  the  lower  parts  of  the 
brain  and  by  the  cord  remain. 


222  HUMAN  PHYSIOLOGY 

each  finger  shall  be  placed.  But  after  long  practice  the 
fingers  move  rapidly  and  without  thought.  By  practice  the 
skilled  swordsman  has  trained  his  nervous  system  so  that 
without  thought  —  so  quickly  that  there  is  not  time  for 
thought  —  his  sword  follows  that  of  his  antagonist  and  turns 
aside  the  thrust. 

As  a  physical  habit  can  be  formed  by  the  repetition  of  an 
act,  so  mental  and  moral  habits  can  be  formed  —  habits  of 
good  work  and  of  poor  work ;  of  honesty  and  dishonesty ;  of 
neatness  and  accuracy,  and  of  carelessness  and  untidiness ; 
habits  of  preparing  lessons  and  of  leaving  them  unprepared. 
All  kinds  of  habits  are  formed  most  readily  in  youth,  and 
it  is  seldom  that,  after  the  age  of  twenty-five  or  thirty,  long- 
established  habits  are  broken.  Indeed,  it  is  difficult  at  any 
time  of  life  to  break  a  habit  that  has  once  been  thoroughly 
formed.  The  pupil  who  is  idle  in  the  third  grade  is  usually 
an  idler  still  in  the  sixth  grade.  The  trifler  in  the  sixth  grade 
is  usually  a  trifler  still  in  the  high  school ;  and  it  would  be 
almost  a  miracle  to  find  a  high  school  drone  who  had  become 
a  capable  and  industrious  college  student. 

Just  what  it  is  in  the  nervous  system  that  makes  it  want 
to  keep  doing  the  same  things  over  again,  is  not  known.  But 
it  is  well  known  that  what  a  person  does  in  youth  determines 
very  largely  what  that  person  will  both  do  and  be  in  his  later 
life.  The  character  is  largely  formed  by  the  habits,  and  there 
is  much  truth  in  the  old  proverb  which  says,  "  Sow  an  act 
and  reap  a  habit;  sow  a  habit  and  reap  a  character." 

Summary.  The  nervous  system  controls  the  body  and  is 
the  organ  of  the  mind. 

Most  of  the  nerve  cells  are  in  the  brain  and  spinal  cord,  but 
a  few  of  them  are  in  ganglia.  A  nerve  cell  and  its  fiber  are 
called  a  neuron.  Nerve  fibers  that  carry  impulses  outward 


THE  NERVOUS  SYSTEM  22$ 

are  efferent  fibers,  and  those  that  carry  them  inward  are 
afferent  fibers.  The  nervous  system  does  a  great  part  of 
its  work  by  acting  as  a  connector  of  the  body  parts.  It  is 
arranged  like  a  telephone  system  in  which  the  spinal  cord 
and  brain  correspond  to  the  central  office. 

The  cerebrum  is  the  largest  division  of  the  brain.  It  is 
divided  into  hemispheres  and  has  many  convolutions  on  its  sur- 
face, to  give  room  for  the  cells  that  are  associated  with  the  mind. 
The  fibers  from  it  cross  in  the  medulla,  so  that  the  two  hemi- 
spheres of  the  cerebrum  are  connected  with  opposite  sides  of 
the  body.  The  cerebrum  is  the  seat  of  the  mind  and  of  the 
sensations,  and  originates  impulses  that  cause  voluntary  motion. 

The  cerebellum  causes  the  muscles  to  keep  a  proper  amount 
of  contraction  and  coordinates  the  movements  of  the  muscles 
of  locomotion.  The  pons  is  a  bridge  between  the  different 
parts  of  the  brain.  The  medulla  connects  the  brain  and  spinal 
cord  and  gives  rise  to  nerves  that  supply  the  head  and  many 
internal  organs,  including  the  heart  and  lungs.  The  function 
of  the  medulla  is  to  transmit  stimuli  and  act  as  a  reflex  center. 
The  spinal  cord  gives  rise  to  many  nerves.  It  conducts 
stimuli  and  is  a  reflex  center. 

In  a  reflex  action  the  impulse  starts  in  an  afferent  nerve, 
passes  inward  to  the  brain  or  cord,  and  comes  out  again  along 
an  efferent  nerve.  Reflexes  are  carried  on  without  thought, 
and  through  them  the  body  is  in  a  great  measure  self -regu- 
lating. Certain  reflexes  may  be  acquired  by  practice,  and 
habits  are  easily  formed.  To  a  large  extent  the  habits  formed 
in  youth  determine  what  the  character  will  be. 

QUESTIONS 

Give  two  functions  of  the  nervous  system.  Where  are  most  of  the 
nerve  cells  found?  What  is  a  ganglion?  an  axis  cylinder?  a  neuron? 


224  HUMAN  PHYSIOLOGY 

What  is  an  afferent  nerve  fiber?  an  efferent  nerve  fiber?  How  is 
an  important  part  of  the  work  of  governing  the  body  done  by  the 
nervous  system?  What  is  the  advantage  in  having  the  nervous 
system  arranged  with  a  central  portion  through  which  all  the  body 
parts  are  connected  ? 

What  are  the  parts  of  the  central  nervous  system?  How  large  is 
the  brain  as  compared  with  the  spinal  cord?  Name  the  three 
divisions  of  the  brain.  How  large  is  the  cerebrum?  How  is  it 
divided?  What  are  the  convolutions?  Where  is  the  gray  matter  of 
the  cerebrum?  Of  what  is  it  composed?  With  what  is  it  as- 
sociated? With  what  part  of  the  body  is  the  right  hemisphere  of 
the  cerebrum  connected?  Where  do  the  fibers  from  the  cerebrum 
cross?  Give  three  functions  of  the  cerebrum. 

Wh'at  is  the  arbor  vitae?  Give  two  functions  of  the  cerebellum. 
What  is  the  result  of  injury  to  the  cerebellum?  Where  is  the  pons? 
Of  what  is  it  composed  and  what  does  it  do?  What  part  of  the  body 
is  supplied  with  nerves  from  the  medulla  ?  Why  does  injury  to  the 
medulla  cause  death  ?  Give  two  functions  of  the  medulla. 

Where  are  the  fibers  in  the  spinal  cord?  the  cells?  What  two 
functions  has  the  cord?  What  is  a  reflex  action?  Give  an  example 
of  one.  What  is  the  great  function  of  the  spinal  cord  in  a  reflex 
action  ? 

Mention  some  reflexes  that  can  be  carried  on  without  the  brain. 
What  does  the  spinal  cord  do  in  these  reflexes  in  addition  to  making 
the  connections?  Does  it  have  intelligence?  Where  are  some 
other  reflex  centers?  What  are  some  of  the  reflexes  that  are  carried 
on  by  them?  Give  some  examples  of  how  the  body  regulates  itself 
through  reflexes. 

What  is  an  acquired  reflex?  Give  examples  of  acquired  reflexes. 
How  are  habits  formed?  Why  is  it  important  that  correct  habits  be 
formed  early  in  life  ? 


CHAPTER   XVII 


EFFERENT  ROOTS 


AFFERENT  ROOTS 


FIG.  103.     The  spinal  cord  and  the  roots  of  a  pair  of  spinal 
nerves. 


THE  NERVOUS   SYSTEM  (Continued) 
NERVES 

The  Cranial  Nerves.  The  twelve  pairs  of  cranial  nerves 
rise  from  the  brain.  The  first  pair  are  the  nerves  of  smell, 
and  the  second  pair  are  the  nerves  of  sight.  The  nerves  of 
taste  and  of  hear- 
ing are  also  cra- 
nial nerves.  In 
general,  the  cra- 
nial nerves  sup- 
ply the  head, 
but  one  pair  of 
nerves  from  the  medulla  goes  to  the  internal  organs  of  the 
body  (page  216). 

Spinal  Nerves.  Thirty-one  pairs  of  spinal  nerves  pass  out- 
ward from  the  spinal  cord  through  openings  between  the 
vertebrae.  Each  spinal  nerve  has  a  ventral  and  dorsal  set  of 
roots.  The  ventral  roots  come  from  the  front  of  the  cord  and 
the  dorsal  roots  from  the  back  of  the  cord.  The  ventral 
roots  contain  the  efferent  fibers,  and  the  dorsal  roots  the 
afferent  fibers.  Outside  of  the  spinal  column  the  roots  unite 
to  form  one  nerve,  which  contains  both  efferent  and  afferent 
fibers. 

Effect  of  cutting  and  stimulating  a  Spinal  Nerve.  The  affer- 
ent impulses  pass  into  the  cord  through  the  dorsal  roots  of  a 

225 


226  HUMAN  PHYSIOLOGY 

spinal  nerve;  the  efferent  impulses  pass  out  of  the  cord 
through  the  ventral  roots.  What  effect  would  it  have  on  the 
part  that  is  supplied  by  a  spinal  nerve,  if  the  nerve  were 
cut  as  in  A  (Fig.  104)?  If  it  were  cut  as  in  /??  as  in  C? 


AFFERENT  ROOT 


AFFERENT  ROOT  AFFERENT  ROOT 


EFFERENT  ROOT  A  EFFERENT  ROOT  -O  -  EFFERENT  ROOT 


FIG.  104.     A  is  a  spinal  nerve  that  has  been  cut ;    B  is  a  spinal  nerve,  with  the 
efferent  root  cut ;   C  is  a  spinal  nerve  with  the  afferent  root  cut. 

A  nerve  impulse  started  in  the  wrong  direction  in  a  nerve 
produces  no  effect.  Suppose  that  by  pinching  the  cut  end 
of  the  nerve  or  by  touching  it  with  an  electric  wire  you  stimu- 
lated it  and  started  an  impulse  in  it.  What  effect  would  it 
have  to  stimulate  the  cut  end  at  a  (Fig.  104)?  at  £?  at  <r? 
at</?  at*?  at/? 

THE   SYMPATHETIC  NERVOUS   SYSTEM 

Nearly  all  the  cells  of  the  central  nervous  system  are  in  the 
brain  and  spinal  cord.  They  are  collected  in  great  centers. 
The  cells  of  the  sympathetic  nervous  system  are  in  ganglia, 
which  are  scattered  through  the  body.  This  system  consists 
chiefly  of  two  chains  of  ganglia,  one  on  either  side  of  the 
spinal  column ;  of  scattered  ganglia  in  many  of  the  internal 
organs,  especially  the  intestine  and  other  abdominal  organs ; 
of  a  great  network  of -fibers  that  connect  all  these  ganglia 
with  each  other  and  with  the  spinal  cord  and  brain ;  and  of 
the  sympathetic  nerves  that  supply  various  organs. 

From  some  of  the  cranial  nerves  and  from  all  of  the  spinal 
nerves,  branches  run  to  and  from  the  sympathetic  ganglia. 
Every  part  of  the  sympathetic  nervous  system  is  thus  con- 


THE  NERVOUS  SYSTEM 


227 


nected  with  the  central  nervous  system,  the 
medulla  and  the  sympathetic  system  being 
especially  closely  connected.  Thus  the  central 
nervous  system  is  able,  through  the  sympa- 
thetic system,  to  reach  the  parts  of  the  body 
that  are  not  supplied  with  nerves  directly  from 
the  brain  and  cord. 

The  Function  of  the  Sympathetic  System.     In 
general  the  sympathetic  system  controls  the  in- 
ternal   organs    (heart 
and  blood  vessels,  di- 
gestive    organs,    kid- 
neys,   etc.)     and    the 
sweat  glands  and  ves- 
sels  of    the    skin.     It 
/«*    ,M  MEDULLA  controls  these  organs 

t  TO  HEART  LUNGS.  AND 

chiefly  through  reflex 
actions,  yet  the 
sympathetic  system  is 
not  an  independent 
system.  It  cannot  do 
its  work  without  the 
central  nervous  sys- 
tem, as  you  will  un- 
derstand when  you 
have  learned  how 
sympathetic  reflexes 
are  carried  out. 


FIG.  106.     Side  view  of  the  sym- 
pathetic nervous  system.    Note  the 


FIG.  105.  The 
two  chains  of 
sympathetic  gan- 


Sympathetic   Re-  slia- 
chain  of  ganglia  Wing  beside  the  flexes.      A    sympathetic     ganglion 

spinal  column,  and  the  great  net-   ^as  noj.  jfo  p0>uuer  to  turn  an  impulse 

r/or^r  mnningt°  ^  ^  back  and  cause  a  reflex  action,  but 


228  HUMAN  PHYSIOLOGY 

when  the  ganglion  receives  an  afferent  impulse,  it  sends  the 
impulse  on  into  the  spinal  cord  or  brain,  where  it  is  started 
back  down  an  efferent  nerve.  The  impulses  go  through 
ganglia  on  their  way  to  and  from  the  cord  and  brain, 
but  the  reflex  centers  lie  in  the  central  system.  Although 
the  central  nervous  system  takes  part  in  the  sympathetic 
reflexes,  yet  we  have  no  consciousness  of  these  reflexes. 
Neither  is  it  possible  for  us  by  a  voluntary  effort  to 
influence  the  internal  organs  through  the  sympathetic  sys- 
tem. This  system  is  connected  with  the  spinal  cord  and  with 
the  lower  centers  of  the  brain,  and  not  with  the  higher  cen- 
ters of  the  brain,  with  which  the  mind  is  associated. 


FIG.  107.   In  the  sympathetic  system  the  nerve  impulses  pass  through  ganglia  on 
their  way  to  and  from  the  cord  and  brain. 

The  Sympathetic  a  Part  of  the  Central  Nervous  System. 
The  entire  nervous  system  works  together  in  governing  the 
body,  and  it  gives  a  wrong  impression  to  speak  of  two 
systems.  The  sympathetic  is,  after  all,  only  a  branch  of 
the  central  nervous  system  that  is  ruled  without  our  knowl- 
edge by  the  cord  and  by  the  lower  centers  of  the  brain. 
It  contains  such  a  network  of  fibers  that  almost  all  the 
internal  parts  of  the  body  are  connected  the  one  with  the 
other,  so  that  it  is  impossible  for  one  of  these  organs  to 
become  deranged  without  affecting  the  other  organs.  The 
organs  thus  "  sympathize"  with  each  other,  and  for  this  reason 
the  nerves  to  these  parts  are  called  the  sympathetic  system. 


THE  NERVOUS  SYSTEM 


229 


THE  NERVOUS   SYSTEMS   OF  OTHER  ANIMALS 

The  great  difference  in  the  nervous  systems  of  the  higher 
and  lower  vertebrates  is  in  the  cerebrum.  In  the  lower 
forms,  as  in  the  fishes,  frogs,  and 
reptiles,  the  cerebrum  is  small 
and  smooth,  and  contains  on  its 
surface  only  a  few  of  the  nerve 
cells  (gray  matter)  that  in  man 
are  associated  with  the  mind. 
In  the  higher  animals,  the  cere- 
brum is  greatly  increased  in 
size,  and  its  surface  becomes 
convoluted,  making  room  for  a 
great  number  of  nerve  cells  on 
its  surface.  As  a  general  state- 
ment, it  is  true  that  intelligence 
increases  with  the  development 
of  the  cerebrum.  The  lower  forms  with  small  cerebrums  are 
stupid,  and  higher  animals  with  larger  and  more  convoluted 
cerebrums  are  more  intelligent.  The  cerebrum  of  man  is  the 
most  highly  developed  of  all,  and  man  is  the  most  intelligent 
of  all  animals. 

HYGIENE  OF  THE  NERVOUS   SYSTEM 

The  nervous  system  is  so  closely  connected  with  all  parts  of 
the  body  that  it  is  of  the  utmost  importance  to  keep  it  in 
health.  Good  food  and  fresh  air  are  necessary  to  the  nerve 
cells,  as  they  are  to  all  other  cells.  In  the  special  hygiene  of 
the  nervous  system,  the  following  points  should  be  noted  : 

Sleep.  Sleep  is  absolutely  necessary  to  the  nervous  sys- 
tem. During  sleep  the  nerve  cells  rest  and  prepare  them- 


FIG.  108.  The  brain  of  a  snake  (A), 
and  of  a  cat  (B). 


230  HUMAN  PHYSIOLOGY 

selves  for  further  work,  and  the  idea  that  it  is  possible  to 
sleep  too  much  is  probably  incorrect.  Babies  should  sleep 
from  fifteen  to  twenty  hours  out  of  the  twenty-four,  older 
children  from  ten  to  fourteen  hours,  and  adults  from  seven  to 
ten  hours.  Occasionally  a  person  is  found  who  keeps  in  good 
health"  on  five  or  six  hours  of  sleep,  and  other  persons  are 
found  who  must  have  eleven  or  twelve  hours.  Most  people 
under  twenty  years  of  age  are  better  off  with  ten  hours  of 
sleep  than  with  eight  or  nine  hours,  and  most  older  persons 
keep  in  better  health  when  they  sleep  nine  full  hours  than 
when  they  sleep  seven  or  eight  hours. 

There  is  no  surer  way  to  undermine  the  health  than  to  stay 
up  late  at  night  and  get  up  early  in  the.  morning,  thus  cutting 
short  the  hours  of  sleep.  One  who  is  doing  this  may  think 
he  is  in  good  health,  but  if  he  will  enter  an  athletic  contest  or 
do  something  else  that  will  really  put  his  nervous  system  to 
the  test,  he  will  find  that  he  is  not  in  the  best  condition.  A 
runner  who  has  been  losing  sleep  has  not  the  slightest  chance 
of  winning  from  others  who  have  had  long  and  regular  hours 
of  sleep.  His  nervous  system  cannot  control  his  muscles 
quickly  and  accurately  enough  to  prevent  his  falling  behind 
in  the  race. 

Tobacco.     The  evil  effects  of  tobacco  on  the  nervous  system  . 
are  generally  recognized.     Its  weakening  effect  on  the  mus- 
cles has  already  been  noted  (page  74),  and  it  seems  to  produce 
this  effect  more  by  interfering  with  the  nervous  regulation  of 
the  muscles  than  by  injuring  the  muscle  cells  themselves. 

Persons  who  use  tobacco  are  often  troubled  with  a  restless- 
ness and  a  jerkiness  of  movement,  so  that  they  cannot  remain 
long  in  any  one  position.  They  are  also  subject  to  more  or 
less  constant  trembling  of  the  extremities,  especially  of  the 
hands.  Men  who  use  tobacco  seldom  have  the  steadiness  of 


THE  NERVOUS  SYSTEM  231 

nerve  required  to  make  expert  marksmen,  and  athletes  who 
are  training  for  contests  of  strength,  endurance,  or  skill  are 
not  allowed  to  use  tobacco  in  any  form. 

The  effects  of  tobacco  on  the  mind  are  more  pronounced 
than  its  effects  on  the  nervous  control  of  the  muscles.  One 
class  at  Yale  University  was  divided  into  four  grades  accord- 
ing to  scholarship.  Only  25  per  cent  of  those  in  the  highest 
division  used  tobacco,  while  85  per  cent  of  those  in  the  lowest 
division  were  tobacco  users.  In  another  class  90  per  cent  of 
the  first  honor  men  were  non-users  of  tobacco. 

In  young  pupils  the  effects  of  tobacco  on  the  mind  are 
much  more  marked  than  are  its  effects  in  older  persons.  In  a 
Chicago  school,  out  of  125  boys  who  smoked,  only  two  were 
able  to  keep  up  with  their  class.  Nine  tenths  of  these  125 
boys  belonged  to  educated,  intelligent  families;  they  had 
been  given  excellent  school  advantages ;  yet  among  them 
were  found  nearly  all  the  boys  who  were  from  two  to  four 
years  older  than  the  average  age  of  the  children  in  their 
grade.  In  all,  there  were  reported  in  Chicago  2402  pupils 
who  were  cigarette  smokers,  and  only  6  per  cent  of  them 
were  able  to  do  the  school  work  of  their  grade.  It  is  hard  to 
believe  but  that  the  use  of  tobacco  had  dulled  the  minds  of 
these  boys  and  had  changed  many  of  them  from  bright, 
active  pupils  into  idling  incompetents. 

Tobacco  also  often  leads  to  moral  degeneration.  Nothing 
is  more  fatal  to  ambition  than  tobacco,  and  to  an  extent  it 
destroys  the  will  power.  A  boy  begins  smoking  a  few  cigar- 
ettes, and  soon  the  habit  has  fastened  itself  on  him  so  firmly 
and  his  will  has  been  so  weakened  that  he  cannot  break  the 
habit,  even  when  he  realizes  that  he  is  injuring  himself.  The 
great  majority  of  boys  who  smoke  cigarettes  are  irritable,  per- 
verse, and  careless  of  the  rights  of  others.  Our  prisons  and 


232 


HUMAN  PHYSIOLOGY 


reformatories  are  filled  with  those  who  began  smoking  cigar- 
ettes in  youth.  What  would  have  been  the  fate  of  each  of 
these  persons  if  he  had  not  used  tobacco,  is  of  course  im- 
possible to  say ;  but  there  is  no  doubt  but  that  many  of 
them  would  have  led  successful  lives  if  it  had  not  been  for 
cigarettes. 

So  well  known  are  the  effects  of  tobacco  on  the  young,  th'at 
in  nearly  all  our  states  and  in  many  foreign  countries,  stringent 
laws  have  been  passed  making  it  a  crime  to  sell  or  give 
tobacco  to  boys  under  a  certain  age.  One  state  has  even 
prohibited  the  use  of  cigarettes  in  any  form  by  old  or  young. 


FIG.  109.  At  the  left  is  a  healthy  nerve  cell  from  a  sympathetic  ganglion.  The 
others  are  nerve  cells  from  one  of  the  sympathetic  ganglia  of  a  man  who  died  of  alco- 
holic paralysis.  Note  the  breaking  down  of  the  cells  that  the  alcohol  has  caused. 

Employers  often  favor  those  who  do  not  use  tobacco,  and 
many  employers  will  have  nothing  to  do  with  tobacco-using 
boys.  The  evil  effects  of  tobacco  are  known  to  the  world, 
and  this  evil  effect  falls  most  heavily  on  the  nervous  system. 

Alcohol.  To  tell  the  exact  effect  of  a  very  small  amount 
of  alcohol  on  the  nervous  system  is  no  more  possible  than  to 
tell  the  exact  effect  of  a  small  amount  of  alcohol  on  any 
other  part  of  the  body.  When  any  considerable  amounts  of 
alcohol  are  taken,  however,  the  entire  nervous  system  is 
deranged.  The  following  effects  are  very  noticeable  when 
alcohol  is  used  to  excess  : 

If  enough  alcohol  is  given  to  an  animal  to  produce  intoxi- 


THE  NERVOUS  SYSTEM  233 

cation,  in  from  ten  to  forty  minutes  the  branches  of  some  of 
the  nerve  cells  will  be  found  to  be  shrunken  and  gathered 
into  little  knots,  and  .certain  granules  that  are  found  in  the 
protoplasm  of  nerve  cells  will  have  broken  down.  In  long- 
continued  excessive  use  of  alcohol,  many  of  the  cells  die,  and 
it  is  also  common  for  nerve  fibers  to  degenerate  and  die, 
causing  paralysis.  Continued  use  of  alcohol  also  causes  a 
thickening  of  the  connective-tissue  membranes  of  the  brain, 
and  of  the  supporting  tissue  within  the  gray  matter  of  the 
brain,  so  that  the  brain  of  a  confirmed  alcoholic  contains 
fewer  nerve  cells  and  more  supporting  tissue  than  does  a 
normal  brain.  In  delirium  tremens,  some  changes  that  are 
not  at  all  understood  occur  in  the  nerve  cells  generally. 
With  such  changes  in  structure  of  the  nervous  tissue,  we 
should  naturally  expect  the  great  disturbances  of  function 
which  alcohol  causes. 

Almost  every  one  is  familiar  with  the  way  the  nervous 
system  loses  control  of  the  muscles  when  it  is  under  the  in- 
fluence of  alcohol.  The  weakening  of  the  muscles  that  fol- 
lows the  use  of  alcohol  (page  74)  seems  to  be  due  more  to 
its  effect  on  the  nervous  system  than  to  the  effect  on  the 
muscles  themselves.  The  nervous  system  is  as  greatly  in- 
fluenced by  alcohol  in  its  other  work,  as  in  its  work  of  regu- 
lating the  muscles ;  the  mind  of  an  intoxicated  person  works 
no  more  accurately  than  his  muscles  work.  Drunkenness 
may  very  properly  be  considered  as  temporary  insanity, 
caused  by  the  poisoning  of  the  nerve  cells  by  alcohol.  De- 
lirium tremens  is  a  condition  in  which  the  cells  have  been  so 
repeatedly  poisoned  that  ideas  are  associated  in  the  most 
grotesque  and  frequently  terrifying  manner. 

The  effects  of  alcohol  on  animals  are  very  marked.  Kittens 
that  were  daily  intoxicated  with  alcohol  lost  all  interest  in 


234 


HUMAN  PHYSIOLOGY 


FIG.  no.     These  are  normal  kittens,  and  they  are  playing  as  healthy  kittens  do. 

play,  cleanliness,  and  mice,  and  showed  no  fear  of  dogs. 
They  ate  and  slept,  but  took  no  interest  in  anything  else, 
acting  strikingly  like  animals  from  which  the  cerebrum  had 
been  removed.  Dogs  that  had  been  given  alcohol  daily  in 
moderate  amounts  showed  the  most  extreme  fear,  howling 


FIG.  in.     These  kittens  have  been  given  alcohol.     They  are  stupid  and  sleepy, 
and  have  lost  all  interest  in  play.     (From  a  photograph  by  Dr.  C.  F.  Hodge.) 


THE  NERVOUS  SYSTEM  235 

and  cringing  when  a  bell  was  rung  or  when  the  floor  was 
struck,  and  awakening  from  their  sleep  to  cower  in  terror  or 
run  and  howl  in  an  agony  of  causeless  fear.  This  timidity 
continued  after  the  giving  of  alcohol  had  been  stopped,  show- 
ing that  the  mental  workings  of  the  brain  had  been  perma- 
nently injured. 

The  results  of  these  experiments  show  the  very  great  effect 
of  alcohol  on  the  mind.  It  is  estimated  that  20  per  cent  of 
insanity  comes  from  this  cause,  and  it  is  proper  to  conclude 
that  just  as  alcohol  injures  the  liver  and  kidneys,  so  it  injures 
the  nerve  tissue;  and  as  it  interferes  with  the  workings  of 
the  liver  and  kidneys,  so  it  interferes  with  the  function  of  the 
nervous  system,  both  in  governing  the  body  and  in  its  work 
as  an  organ  of  the  mind. 

Summary.  The  twelve  pairs  of  cranial  nerves  rise  from 
the  brain.  They  supply  the  head  and  many  of  the  internal 
organs.  The  thirty-one  pairs  of  spinal  nerves  rise  in  the 
spinal  cord.  Each  nerve  has  a  set  of  ventral  roots  that  con- 
tain the  efferent  fibers  and  a  set  of  dorsal  roots  that  contain 
the  afferent  fibers. 

The  sympathetic  nervous  system  consists  of  a  network 
of  ganglia  and  fibers.  It  controls  by  reflexes  the  internal 
organs,  the  blood  vessels,  and  the  sweat  glands.  It  is  con- 
nected with  the  central  nervous  system  and  cannot  carry  on 
its  work  alone.  It  is  called  the  sympathetic  system  because 
by  it  all  the  internal  organs  are  connected  and  through  it 
they  "  sympathize  "  with  each  other. 

Intelligence  increases  with  the  development  of  the  cere- 
brum. The  lower  vertebrates  have  small,  smooth  cerebrums 
and  the  higher  vertebrates  have  larger  and  more  convoluted 
cerebrums.  The  human  cerebrum  is  the  most  highly  devel- 
oped of  all. 


236  HUMAN  PHYSIOLOGY 

Because  the  nervous  system  is  directly  connected  with  all 
parts  of  the  body,  it  is  very  important  to  keep  it  in  health. 
The  special  need  of  the  nervous  system  is  sleep,  without 
enough  of  which  we  cannot  have  good  health. 

Tobacco  interferes  with  the  nervous  control  of  the  muscles. 
It  also  dulls  the  mind.  It  is  especially  harmful  to  the  young, 
as  is  shown  by  the  fact  that  only  6  per  cent  of  2402  cigarette 
smokers  in  the  Chicago  public  schools  were  able  to  do  their 
school  work.  Another  effect  of  tobacco  is  a  weakening  of 
the  moral  nature. 

Alcohol  affects  the  structure  of  nerve  tissue,  the  excessive 
use  of  alcohol  causing  many  of  the  nerve  cells  and  fibers  to 
die.  It  also  affects  the  function  of  nerve  tissue,  intoxication 
causing  the  nervous  system  to  lose  its  control  of  the  muscles 
and  its  mental  power.  The  minds  of  animals  are  perma- 
nently injured  by  alcohol,  and  among  human  beings  about 
20  per  cent  of  insanity  is  caused  by  it. 


QUESTIONS 

How  many  pairs  of  cranial  nerves  are  there  ?  Where  do  they  rise  ? 
What  part  of  the  body  do  they  supply? 

How  many  pairs  of  spinal  nerves  are  there?  Where  do  they  rise? 
What  kind  of  fibers  are  in  the  dorsal  roots  ?  the  ventral  roots  ? 

Of  what  does  the  sympathetic  nervous  system  consist?  How  is  the 
central  nervous  system  connected  with  it?  What  part  of  the  body 
does  it  control?  Explain  how  a  sympathetic  reflex  is  carried  out. 
Are  we  conscious  of  these  reflexes?  Can  we  control  them?  Why  is 
this  part  of  the  nervous  system  called  the  sympathetic  system? 

What  is  the  great  difference  in  the  nervous  systems  of  the  higher 
and  lower  vertebrates  ?  What  increases  with  the  development  of  the 
cerebrum  ? 


THE  NERVOUS  SYSTEM  237 

How  much  sleep  is  needed  by  persons  of  different  ages  ?  What  is 
said  of  the  importance  of  sleep? 

What  effect  has  tobacco  on  the  muscles?  How  does  it  produce 
this  effect?  What  did  investigations  at  Yale  University  show  in 
regard  to  the  effects  of  tobacco  on  the  students?  How  many  of  the 
125  cigarette  smokers  in  one  Chicago  public  school  kept  up  their 
school  work?  What  per  cent  of  the  cigarette  smokers  in  all  the 
schools  investigated  did  so?  What  effect  has  tobacco  on  the  am- 
bition? on  the  will  power?  As  a  rule,  are  cigarette  smokers  worried 
about  their  own  condition  and  anxious  to  do  better?  Why  have  laws 
been  made  against  selling  cigarettes?  Why  do  employers  favor  boys 
who  do  not  use  tobacco? 

What  is  the  effect  on  the  nerve  cells  of  an  animal  of  sufficient  alco- 
hol to  cause  intoxication  ?  How  quickly  does  it  produce  this  effect  ? 
What  effect  has  long-continued  and  excessive  use  of  alcohol  on  nerve 
tissue  ?  on  the  supporting  tissue  of  the  brain  ?  What  effect  has  alcohol 
on  the  nervous  control  of  the  muscles  ?  on  the  mental  workings  of  the 
nervous  system  ? 

What  effect  had  daily  intoxication  on  kittens?  What  effect  had 
moderate  amounts  of  alcohol  on  the  minds  of  dogs  ? 


A  reflex  movement  (Fig.  101)  is  quicker  than  the  movement 
would  be  if  the  impulse  had  to  go  to  the  brain.  Explain  why.  What 
advantage  is  there  in  having  the  body  governed  by  reflexes  that 
require  no  attention  from  the  mind? 

When  the  "  funny  bone  "  is  struck,  a  nerve  in  the  arm  is  crushed 
against  the  bone.  What  part  of  the  body  is  affected  ?  Explain  why. 
Persons  who  have -had  a  limb  amputated  sometimes  complain  of 
pain  in  the  limb.  What  causes  this  sensation?  Where  is  the 
trouble  in  a  paralytic  stroke? 


CHAPTER   XVIII 

THE  EFFECTS  OF  ALCOHOL  ON  THE  HUMAN  BODY 

THE  question  of  the  use  of  alcoholic  drinks  is  one  that  con- 
tinually agitates  our  nation,  and  indeed  has  been  receiving, 
for  many  years,  the  serious  attention  of  the  whole  civilized 
world.  The  opponents  of  alcohol  insist  that  it  is  the  chief 
cause  of  poverty  and  crime,  and  they  urge  against  alcohol 
the  physiological  argument  that  it  injures  the  body.  Other 
persons  maintain  that  alcohol,  in  moderate  quantities,  is 
beneficial  to  the  body. 

We  have  already  learned  something  of  the  effects  of  alcohol 
on  many  of  the  different  organs  of  the  body.  The  human 
body,  however,  is  more  than  a  collection  of  organs.  It  is 
one  whole,  and  any  physiological  question  must  be  looked  at 
from  the  standpoint  of  the  body  as  a  whole.  In  this  chapter 
we  shall  take  up  the  effects  of  alcohol  on  the  body  from  a 
more  general  view  point. 

What   is  Alcohol  ?     Alcohol  is  a  substance  formed  from 

sugar  by  a  small  plant  called 
yeast.  When  yeast  grows  in 
water  in  which  sugar  is  dissolved, 
it  digests  or  ferments  the  sugar, 
breaking  it  up  into  water,  carbon 

FIG.  112.   Yeast  plants.  dioxid,  and  alcohoL       The  alcohol, 

like  the  carbon  dioxid,  is  poisonous  to  the  yeast  if  present  in 
large  quantities. 

Alcoholic  Drinks.  The  most  common  alcoholic  drinks  are 
wine,  cider,  beer,  and  distilled  liquors.  Wine  and  cider  are 

238 


EFFECTS  OF  ALCOHOL   ON  THE  HUMAN  BODY       239 

made  by  allowing  yeast  to  ferment  the  sugar  in  fruit  juice. 
If  it  is  apple  juice  that  is  fermented,  the  product  is  cider.  If 
grape  juice  is  fermented,  the  product  is  wine.  Beer  is  made 
by  allowing  the  yeast  to  ferment  sugar  from  grain.  The 
starch  in  the  grain  is  first  changed  to  sugar  by  sprouting 
the  grain,  after  which  it  is  ready  to  be  fermented  by  the  yeast.1 

Brandy  is  manufactured  by  distilling  fermented  fruit  juice. 
Whisky  is  made  by  distilling  the  fermented  material  from 
grain  or  potatoes,  and  rum  by  distilling  fermented  molasses. 
Beer  contains  on  an  average  about  5  per  cent  of  alcohol, 
wine  contains  about  10  per  cent  of  alcohol,  and  distilled 
liquors  contain  about  50  per  cent  of  alcohol. 

Alcohol  and  Length  of  Life.  If  alcohol  as  it  is  commonly 
used  is  beneficial  to  the  body,  drinkers  should  live  longer 
than  those  who  abstain  from  alcohol.  If  alcohol  injures  the 
body,  we  should  expect  abstainers  to  be  longer  lived  than 
drinkers.  The  best  possible  way,  therefore,  of  settling  the 
question  as  to  whether  alcohol  injures  or  benefits  the  body  is 
to  compare  the  death  rates  of  drinkers  and  of  abstainers. 

The  United  Kingdom  Temperance  and  General  Provident 
Institution  is  a  life  insurance  company  of  London,  England. 
For  more  than  fifty  years  this  company  has  kept  separate 
lists  of  the  moderate2  drinkers  and  abstainers  among  its  policy 

1  In  distilling  liquors,  the  liquid  (the  fruit  juice  or  the  water  in  which  the 
grain  has  been  soaked)  that  contains  the  fermented  sugar  is  heated,  and  the 
vapor  that  comes  from  it  is  caught  and  condensed.     The  alcohol  in  the  liquid  is 
changed  to  vapor  more  easily  than  the  water,  and  the  liquors  that  are  manufac- 
tured in  this  way  are  strong  in  alcohol. 

2  All  insurance  companies  refuse  to  accept  heavy  drinkers,  and  they  reject 
many  persons  who  are   very  moderate  drinkers  indeed.     The  above   statistics, 
therefore,  apply  only  to  those  who  were  moderate  drinkers  at  the  time  they  were 
insured.     Some  of  them   may  later  have  become  excessive  drinkers,    but  if  all 
drinkers  were  included  in  the  statistics,  the   death  rate  among  the  alcohol  users 
would  be  very  much  higher  than  is  here  shown. 


240  HUMAN  PHYSIOLOGY 

holders.  Its  records  show  that  for  every  74.3  deaths  among 
abstainers,  there  are  100.4  deaths  among  the  drinkers.  The 
death  rate  is,  therefore,  35  per  cent  higher  among  the 
users  than  among  the  non-users  of  alcohol.  Many  other  life 
insurance  companies  have  kept  similar  records,  and  in  every 
case  the  death  rate  is  from  25  to  50  per  cent  higher 
among  the  drinkers  than  among  the  abstainers.  These 
averages  have  been  made  up  from  records  including  many 
thousands  of  lives,  and  there  is  no  doubt  of  their  correct- 
ness. They  have  been  examined  with  great  care  to  see 
if  there  was  any  reason  other  than  the  use  of  alcohol  why 
the  drinking  man  should  die  earlier  than  the  non-drinker. 
No  such  reason  can  be  found,  and  it  is  certain  that  the 
users  of  alcohol  fail  to  live  as  long  as  those  who  do  not  use 
alcohol,  because  the  alcohol  weakens  and  injures  the  body. x 

Alcohol  and  Tuberculosis.  We  have  already  seen  (page  171) 
that  alcohol  lowers  the  power  of  the  body  to  resist  disease 
germs.  The  relation  of  alcohol  to  tuberculosis  deserves 
special  mention. 

In  France,  the  districts  drinking  12.5  liters  of  wine  per  capita 
had  annually  3.3  deaths  from  tuberculosis  for  each  one  thou- 
sand inhabitants.  The  districts  drinking  35.4  liters  of  wine  per 
capita  had  annually  10.8  deaths  from  tuberculosis  for  each  one 
thousand  inhabitants.  In  the  sanatoria  for  consumptives  at 
Loslau,  Germany,  in  1899,  30  per  cent  of  the  patients  were 
avowed  alcoholics,  37  per  cent  were  moderate  drinkers,  27  per 
cent  were  occasional  drinkers,  and  only  6  per  cent  were  total  ab- 
stainers. According  to  estimates  made  in  France,  10.3  per  cent 
of  the  children  of  drunkards  suffer  from  tuberculosis,  while  only 
1 .8  per  cent  of  the  children  of  total  abstainers  have  tuberculosis. 

1  A  German  society  offers  a  reward  of  one  thousand  marks  to  any  one  who 
will  prove  the  incorrectness  of  the  figures  that  have  led  to  this  conclusion. 


EFFECTS  OF  ALCOHOL   ON  THE  HUMAN  BODY       241 

Statistics  like  these  show  clearly  that  alcohol  users  are 
especially  subject  to  tuberculosis.  So  thoroughly  established 
and  so  important  is  this  fact,  that  in  Paris,  in  1905,  the  Inter- 
national Tuberculosis  Congress,  whose  members  include  the 
most  learned  bacteriologists  and  physicians  in  all  the  world, 
adopted  the  following  resolution :  "  We  strongly  emphasize 
the  necessity  and  importance  of  combining  the  fight  against 
tuberculosis  with  the  struggle  against  alcoholism." 

The  Relation  of  Alcohol  to  Insanity.  The  great  increase  in 
recent  years  of  the  number  of  the  insane  has  excited  alarm, 
and  considerable  time  has  been  devoted  to  studying  the  causes 
of  insanity.  From  a  careful  study  of  the  causes  bringing  on 
insanity  in  the  patients  in  all  the  asylums  in  England,  Wales, 
and  Ireland,  it  is  estimated  that  alcohol  causes  about  20 
per  cent  of  all  insanity.  In  England,  personal  intemperance 
(intemperance  of  the  insane  person  himself)  causes  nearly 
15  per  cent  of  insanity,  and  intemperance  of  the  parents 
causes  enough  more  to  bring  the  total  to  about  20  per  cent. 
When  one  thinks  of  the  very  great  effect  that  alcohol  has  on 
nerve  tissue,  and  of  the  way  it  affects  the  working  of  the 
mind,  it  does  not  seem  at  all  strange  that  continued  drinking 
should  bring  on  insanity. 

Alcohol  and  Heredity.  Whether  or  not  the  children  of 
those  using  alcohol  are  affected  by  the  drinking  of  their  par- 
ents is  a  question  that  cannot  be  neglected.  That  children 
are  very  greatly  affected  by  drunkenness  in  their  parents,  the 
following  facts  make  certain : 

Two  pairs  of  dogs,  as  nearly  alike  as  possible,  were  selected. 
One  pair  was  given  alcohol  in  their  food,  and  the  other  pair 
had  the  same  food  and  care,  without  alcohol.  Of  twenty- 
three  puppies  of  the  pair  of  dogs  that  had  alcohol,  nine  were 
deformed,  ten  were  born  dead,  and  only  four  lived.  The 


242  HUMAN  PHYSIOLOGY 

other  pair  of  dogs  in  the  same  time  raised  forty-five  puppies, 
four  of  which  were  deformed  and  forty-one  of  which  lived. 
Thus,  only  17.4  per  cent  of  the  puppies  born  to  the  alcoholic 
dogs  lived,  while  90.2  per  cent  of  the  much  larger  number 
born  to  the  other  dogs  lived. 

Much  the  same  effect  is  produced  in  human  families  by 
alcohol.  In  ten  alcoholic  families  investigated,  there  were  fifty- 
seven  children.  Of  "these  children,  ten  were  deformed,  six 
were  idiots,  six  were  epileptics,  twenty-five  failed  to  live,  and 
only  ten  of  the  fifty-seven,  or  17  per  cent,  were  normal 
and  healthy.  In  ten  families  not  using  alcohol  that  were  in- 
vestigated, there  were  sixty-one  children.  Of  these,  two  were 
deformed,  five  failed  to  live,  and  fifty-four,  or  88.5  per  cent, 
were  normal  and  healthy.  One  investigator  estimates  that 
only  about  17.5  per  cent  of  the  children  of  drunkards  are 
physically  sound;  another  places  the  percentage  at  11.7  per 
cent ;  and  still  another  reports  that  of  the  children  of  drunken 
parents  examined  by  him,  not  more  than  6.2  per  cent  were 
strong  and  well.  These  facts  show  that  the  bodies  of  children 
are  affected  by  the  intemperance  of  their  parents. 

The  minds  of  children  are  also  affected  by  the  drinking  of 
parents,  as  the  following  facts  show : 

Of  8624  children  of  drunken  parents,  53  per  cent  were 
mentally  defective,  while  of  13,323  children  of  sober  parents, 
only  i o.i  per  cent  were  unable  to  keep  up  with  their  school 
work.  Of  children  whose  ancestors  had  been  free  from 
alcoholic  taint  for  three  generations,  96  per  cent  were  pro- 
ficient in  school  work,  while  of  those  who  had  three  gen- 
erations of  alcoholic  ancestors,  only  23  per  cent  were  able  to 
keep  up  with  their  classes,  and  76  per  cent  had  some 
nervous  trouble. 

We  thus  see  that  the  evil  effects  of  alcohol  on  both  mind 


EFFECTS   OF  ALCOHOL    ON  THE  HUMAN  BODY       243 

and  body  are  inherited.  Professor  Welch  of  Johns  Hopkins 
University  says,  "  The  brunt  of  the  evil  heritage  of  alcohol 
falls  on  the  nervous  system  of  the  second  generation." 

Alcohol  and  Character.  The  relation  of  the  body  to  the 
mind  is  not  understood.  We  do  not  know,  therefore,  how 
drugs  affect  the  mind  and  character  of  a  person,  but  we  do 
know  that  drugs  can  do  this.  The  continued  use  of  opium 
will  change  an  upright  and  honorable  person  into  a  shameless 
falsifier.  Cocaine  sometimes  turns  mere  boys  into  desperate 
criminals,  who  do  not  shrink  from  robbery  and  murder. 
Alcohol  also  has  a  great  effect  on  the  character.  By  intoxi- 
cation, some  mild  and  kind  men  are  changed  into  cruel  and 
dangerous  persons,  and  the  breaking  down  of  the  will  power 
and  character  in  confirmed  drunkards  is  something  with 
which  many  people  are  familiar. 

The  following  facts  show  that,  in  the  opinion  of  business 
men,  drinking  renders  men  on  the  whole  less  faithful,  honest, 
and  efficient.  Bonding  companies  are  suspicious  of  drinking 
men,  and  often  refuse  to  furnish  bonds  for  men  who  frequent 
saloons.  The  Fifth  Avenue  National  Bank  of  New  York 
City  has  for  thirty  years  forbidden  even  its  clerks  and  mes- 
senger boys  to  drink  in  saloons  and  barrooms.  Many  large 
railroads  refuse  to  employ  drinking  men  in  their  operating 
departments,  and  some  of  them  refuse  to  employ  drinkers 
even  as  bookkeepers  or  ticket  agents.  Shrewd  business 
men  everywhere,  in  employing  men,  give  the  preference  to 
abstainers  over  drinkers.  Any  young  man  seeking  employ- 
ment in  a  responsible  position  will  soon  learn  that  one  of 
the  first  questions  asked  an  applicant  is  whether  or  not  he 
drinks. 

Conclusion.  We  find  that  alcohol  shortens  life;  that  it 
makes  the  users  of  it  more  susceptible  to  germ  diseases,  the 


244  HUMAN  PHYSIOLOGY 

relation  of  alcohol  drinking  to  tuberculosis  showing  this  in 
a  striking  way ;  that  alcohol  causes  a  considerable  amount  of 
insanity,  and  that  the  drinking  of  parents  has  a  very  inju- 
rious effect  on  the  bodies  and  minds  of-  their  children.  We 
also  find  that  alcohol  has  a  tendency  to  destroy  the  will 
power  and  the  character  of  those  who  use  it. 

These  are  facts  that  must  be  faced  by  any  one  investi- 
gating the  effects  of  alcohol  on  the  human  body.  The  only 
answer  that  can  be  made  to  these  facts  is  that  it  is  the  abuse 
and  not  the  use  of  alcohol  that  works  all  this  evil.  This  is  a 
question  that  need  not  be  discussed  here,  for  practically  every 
one  who  uses  alcohol  at  all  uses  too  much  of  it  (page  131). 
When  it  is  used  as  mankind  uses  it,  its  effects  are  the  evil 
effects  given  above. 

QUESTIONS 

How  is  alcohol  formed?  What  is  cider?  wine?  beer?  How  are 
distilled  liquors  manufactured?  How  much  alcohol  is  in  wine?  in 
beer?  in  distilled  liquors? 

What  figures  are  given  as  to  the  death  rates  of  drinkers  and 
abstainers?  Why  must  these  figures  be  regarded  as  reliable? 

What  reasons  are  there  for  thinking  that  in  France  wine  drinkers 
are  especially  subject  to  tuberculosis?  What  facts  from  Germany 
indicate  that  alcohol  increases  consumption?  What  effect  has 
alcohol  drinking  on  the  amount  of  tuberculosis  among  the  children 
of  the  drinkers?  What  is  the  opinion  of  the  International  Tuberculosis 
Congress  in  regard  to  the  connection  between  alcoholism  and 
tuberculosis  ? 

What  per  cent  of  insanity,  according  to  estimates  made  in  England, 
is  due  to  alcohol?  Tell  something  of  the  effects  of  alcohol  on  the 
children  of  the  drinkers.  What  effect  does  alcohol  often  have 
on  the  character?  What  facts  show  that  business  men  consider 
alcohol  users  less  trustworthy  than  non-drinkers  ? 


CHAPTER    XIX 

THE   SPECIAL   SENSES  :  Touch,  Taste,  Smell,  and  Hearing 

PART  of  the  nerve  impulses  that  are  carried  into  the  brain 
cause  reflex  actions ;  part  of  them  cause  sensations.  It  is 
difficult  to  describe  a  sensation,  but  we  have  all  experienced 
sensations  of  light,  sound,  touch,  heat,  cold,  and  'hunger. 
There  is,  therefore,  no  difficulty  in  understanding  the  mean- 
ing of  the  term. 

General  Sensations.  Hunger  is  caused  by  afferent  im- 
pulses from  the  stomach,  and  thirst  by  impulses  from  the 
pharynx.  Afferent  impulses  from  the  muscles  (for  every 
muscle  has  great  numbers  of  afferent  as  well  as  efferent  nerve 
fibers  ending  in  it)  cause  the  sensation  of  tiredness,  and  other 
impulses  give  rise  to  feelings  of  pain,  nausea,  and  other  sen- 
sations. These  impulses  rise  within  the  body;  they  originate 
because  of  some  condition  of  the  body,  and  they  cause  what 
are  called  the  general  sensations.  Most  (but  not  all)  of  the 
general  sensations  are  caused  by  impulses  that  come  from  all 
parts  of  the  body. 

Special  Sense  Organs.  In  some  parts  of  the  body  are 
special  sense  organs.  In  these  the  afferent  nerve  fibers  end 
in  such  a  way  that  they  are  stimulated  from  without  the  body. 
The  sense  organs  are  the  eye,  the  ear,  the  nose,  the  epithelium 
of  the  tongue  and  mouth,  and  the  skin.  The  nerves  in  the 
eye  are  stimulated  by  light ;  the  nerves  in  the  ear  by  sound 
waves  in  the  air ;  the  nerves  of  smell  by  odors ;  the  nerves  of 

245 


246 


HUMAN  PHYSIOLOGY 


taste  by  substances  dissolved  in  the  mouth;  and  the  nerves 
in  the  skin  by  touching  objects,  and  by  heat  and  cold.  The 
impulses  that  are  thus  started  in  these  nerves  travel  up  to 
the  brain  and  cause  sensations  of  light,  sound,  smell,  taste, 
and  touch.  Seeing,  hearing,  smelling,  tasting,  and  feeling  are 
the  five  special  senses,  and  by  these  senses  we  learn  all  that 
we  know  of  the  world  about  us. 

TOUCH 

Afferent  Nerve  Endings  in  the  Skin.     The  upper  surface 
of  the  dermis  is  thrown  into  papillae  that  stand  up  like  little 


FIG.  113.  Afferent  nerve  endings.  A  shows  a  nerve  fiber  in  the  skin  ending  at 
the  bases  of  tactile  cells.  B  shows  a  nerve  fiber  with  free  endings  among  the  cells  of 
the  skin.  The  nerves  of  glands  and  of  involuntary  muscles,  and  the  afferent  nerves 
of  voluntary  muscles,  end  in  this  way.  C  shows  a  nerve  fiber  ending  in  a  bulb  of 
connective  tissue.  Many  nerve  endings  of  this  kind  are  found  in  the  lower  layers  of 
the  skin,  and  in  the  internal  parts  of  the  body. 


mountain  peaks  under  the  epidermis.     Some  papillae  of  the 
skin  (Fig.  93)  contain  only  blood  vessels,  but  in  other  papillae 


THE  SPECIAL   SENSES  247 

tactile  corpuscles  (Fig.  94)  are  found.  These  are  small,  oval 
bodies,  in  which  one  or  several  nerves  of  touch  end.  The 
tactile  corpuscles  are  especially  abundant  in  the  fingers  and 
toes. 

Other  nerves  of  touch  branch  at  the  ends,  and  have  on  the 
tip  of  the  branch  a  little  saucer-like  expansion  that  fits 
around  the  base  of  an  epidermal  cell.  Such  a  cell  is  called  a 
tactile  cell.  Still  others  of  the  afferent  nerve  fibers  of  the 
skin  end  in  many  small  free  branches  among  the  epidermal 
cells. 

How  we  feel.  When  we  touch  anything,  the  epidermis  is 
pressed  down  on  the  ends  of  the  nerves  of  touch.  This 
starts  an  impulse  up  the  nerve  to  the 
brain,  and  causes  a  sensation  of  feeling. 
If  all  the  nerve  endings  in  the  skin  that 
is  being  touched  have  the  same  amount 
of  pressure  on  them,  we  know  that  we 
are  feeling  a  smooth  surface.  If  some 
of  them  are  being  pressed  harder  than 
others,  we  know  that  the  surface  is 
rough.  We  know  what  part  of  the  body 
it  is  that  is  touching  an  object  because  we  know  which 
nerves  are  bringing  the  impulses.  We  know  whether  the 
object  is  large  or  small  by  the  amount  of  skin  that  is  touching 
it,  and  by  the  distance  that  we  must  move  the  hands  to  pass 
them  over  it.  The  mind  is  thus  able  to  judge  of  many  things 
by  the  nerve  impulses  that  come  to  it  through  the  nerves  of 
touch.  That  it  may  form  mistaken  judgments  from  these 
impulses,  you  can  prove  by  crossing  your  fingers  (Fig.  114) 
and  rubbing  the  point  of  your  nose  so  that  it  will  touch  the 
outer  edge  of  one  finger  and  the  inner  edge  of  another  finger. 
It  will  seem  as  though  you  had  two  noses,  because  ordinarily 


248  HUMAN  PHYSIOLOGY 

it  takes  two  objects  to  touch  the  fingers  on  their  edges  as  the 
nose  is  touching  them,  and  the  mind  has  come  to  think  that 
there  are  two  objects  when  impulses  come  from  these  points 
at  the  same  time. 

Different  Kinds  of  Afferent  Nerves  in  the  Skin.  In  the  skin 
are  nerves  that  are  stimulated  by  touch,  others  that  are  stim- 
ulated by  heat,  and  others  that  are  stimulated  by  cold. 
Whether  there  are  special  nerves  of  pain,  or  whether  any 
afferent  nerve  fiber,  if  stimulated  in  the  wrong  way,  will 
cause  pain,  is  not  known.  When  the  epidermis  is  removed, 
as  by  a  burn,  all  sensations  of  touch,  heat,  and  cold  are  lost, 
and  only  sensations  of  pain  come  from  the  part.  That  the 
nerves  in  the  skin  do  not  all  do  the  same  kind  of  work  you 
can  easily  prove  by  the  following  experiment : 

Fill  a  small  test  tube  with  warm  water,  or  warm  the  end  of  a  wire 
or  other  piece  of  metal,  and  pass  it  slowly  over  the  skin  of  the  fore- 
arm. In  certain  spots  you  will  feel  a  sensation  of  warmth.  Mark 
these  places  by  small  drops  of  ink,  and  then  pass  a  cold  object  over 
the  same  area  of  skin.  Note  that  the  nerves  for  feeling  cold  are  not 
in  the  same  place  as  the  heat  nerves.  Also  note  that  nerves  of  touch 
are  found  where  there  are  neither  heat  nor  cold  nerves. 

Where  the  Sense  of  Feeling  is  Best  In  some  parts  of  the 
skin  the  nerve  endings  are  very  abundant,  and  in  these 
places  the  sense  of  touch  is  acute.  In  the 
tip  of  the  tongue  it  is  most  acute  of  all.  It 
is  also  very  highly  developed  in  the  lips,  in 
the  tip  of  the  nose,  and  in  the  finger  tips. 
Thrust  two  pins  through  a  thin  piece  of 
cork  (Fig.  115)  and  touch  them  to  the  fin- 
ger tip.  Here  you  can  feel  the  two  points 
when  they  are  only  one  twelfth  of  an  inch 
apart.  But  if  you  touch  them  to  the  back 
of  the  hand  or  forearm,  they  will  feel  like  one  point  unless  you 


THE  SPECIAL  SENSES  249 

place  them  much  farther  apart.  On  the  tip  of  the  tongue  we 
can  distinguish  two  objects  that  are  only  one  twenty-fifth  of 
an  inch  apart,  while  on  the  back  of  the  body  two  objects  must 
be  separated  by  two  and  one  half  inches  before  we  can  tell 
whether  one  or  two  points  are  touching  us.  The  following 
is  an  interesting  experiment : 

Thrust  two  pins  through  a  piece  of  cork,  and  while  some  member 
of  the  class  is  blindfolded,  or  looking  the  other  way,  touch  his  skin  on 
the  finger  tips,  back  of  the  hand,  forearm,  lips,  cheek,  neck,  etc. 
Sometimes  use  one  pin  and  sometimes  two,  and  measure  how  far 
apart  the  two  must  be  separated  before  they  can  be  distinguished  on 
the  different  parts  of  the  body. 

TASTE 

The  nerves  of  touch  are  all  over  the  body,  but  the  nerves 
of  taste  end  only  in  the  tongue  and  in  the  epithelium  l  of  the 
back  part  of  the  mouth.  The  taste  nerves  branch  out  and 
end  free  among  the  epithelial  cells,  and  in  some  places  in  the 
tongue  they  end  in  a  special  way  in  little 
bodies  that  are  called  taste  buds.  A  taste 
bud  is  composed  of  an  outer  circle  of  long 
cells,  set  edge  to  edge,  as  the  staves  are 
arranged  in  a  barrel.  It  is  buried  in  the 
epithelium  of  the  tongue,  and  at  the  tip  of 
the  bud  is  a  small  opening  out  into  the 
mouth.  Within  the  bud  are  long,  slender  FIG.  116.  A  taste  bud. 
taste  cells,  the  tips  of  which  stand  up  out 
of  the  opening  in  the  end  of  the  bud.  Within  the  taste  bud 
the  nerves  of  taste  are  connected  with  the  taste  cells. 

Before  anything  can  be  tasted,  it  must  first  be  dissolved. 
Then  the  little  molecules  of  the  substance  work  down  in 

1  The  outer  layer  of  cells  in  a  mucous  membrane  is  called  the  epithelium. 
It  corresponds  to  the  epidermis  of  the  skin. 


250 


HUMAN  PHYSIOLOGY 


among  the  taste  cells  and  so  affect  them  that  they  start  im- 
pulses in  the  nerve  fibers  behind  them.  These  impulses  go 
to  the  brain  and  cause  sensations  of  taste. 


SMELL 

The  olfactory  nerves,  or  nerves  of  smell,  end  in  the  lining  of 
the  upper  front  part  of  the  nasal  cavities.     In  the  mucous 

membrane  of  these  parts  are  long, 
slender  cells  called  olfactory  cells, 
They  lie  between  the  epithelial 
cells,  and  their  outer  ends  are  di- 
vided into  fine  cilia-like  processes. 
From  the  inner  end  of  the  olfactory 
cells  nerve  fibers  pass  to  the  brain. 
The  olfactory  cells  are  in  reality 

FIG.   117.     The  olfactory  nerves.    nerve    ceHs    that    have    grown    down 

from  the  brain  above,  and  they  are  the  only 
nerve  cells  in  the  body  that  are  exposed  to 
the  outside  world. 

How  we  smell.  From  anything  that  has 
an  odor,  molecules  are  flying  off  into  the 
air.  These  molecules  pass  into  the  nasal 
chamber,  come  into  contact  with  the  olfac- 
tory cells,  and  there  cause  changes  that 
start  impulses  up  the  olfactory  nerves. 
Drawing  the  air  up  into  the  nose  brings 
the  molecules  up  to  the  olfactory  cells,  and 
we  therefore  sniff  the  air  when  we  wish  to 
smell  anything. 

In  certain  animals  the  sense  of  smell  is 
much  more  highly  developed  than  it  is  the  ciiia-iike processes 

0  ,  .    j         r    j  r    11  on  them  are  the  olfac' 

m  man.     Some  kinds  of  dogs  can  follow    toryceiis 


TO  BRAIN 

FIG.  118.  A  por- 
tion of  the  olfactory 
mucous  membrane. 
The  slender  cells  with 


THE  SPECIAL  SENSES  251 

the  track  of  an  animal  or  man  many  hours  after  the  trail  has 
been  made,  and  bees  and  some  other  insects  are  also  far 
more  keen-scented  than  is  man. 

Care  of  the  Olfactory  Organ.  Inflammation  destroys  the 
delicate  olfactory  cells,  and  when  they  have  been  destroyed 
they  are  not  renewed.  Inhaling  dust  is  a  common  cause  of 
inflammation  of  the  mucous  membrane  of  the  nose,  and  taking 
cigarette  smoke  into  the  nose  is  very  injurious  to  the  olfactory 
cells.  Catarrh  should  have  medical  treatment,  for  by  it  the 
sense  of  smell  is  partially  destroyed  in  many  persons,  and  it 
may  lead  to  more  serious  diseases. 

HEARING 

Hearing  is  caused  by  waves  of  air  striking  against  the  ear. 
In  order  to  understand  this  subject,  it  is  necessary  to  under- 
stand something  of  the  nature  of  air.  In  solid  bodies,  the 
molecules  cannot  move  about  from  one  place  to  another.  In 
liquids,  the  molecules  move  about  and  slip  over  each  other, 
but  they  do  not  separate.  In  gases,  the  molecules  are  not 
held  together,  but  separate  and  fly  off  from  each  other. 

The  air  is  a  mixture  of  gases  (page  178),  and  if  the  air 
molecules  were  visible,  you  would  see  the  molecules  of  the 
different  gases  dancing  and  flying  about  and  striking  against 
each  other.  When  the  wind  blows,  the  molecules  are  flying 
along.  When  the  wind  pushes  against  you,  the  many  little 
molecules  of  which  the  air  is  composed  are  flying  against  you 
and  striking  you.  In  a  great  gale  the  air  may  be  traveling 
at  the  rate  of  a  mile  a  minute,  and  in  very  great  storms  it 
may  even  have  a  speed  of  two  miles  a  minute.  With  a 
speed  like  this,  its  molecules  strike  objects  in  their  path  with 
tremendous  force,  uprooting  trees,  carrying  away  houses,  and 
overturning  large  and  heavy  objects. 


252 


HUMAN  PHYSIOLOGY 


Sound  Waves.  When  you  throw  a  stone  into  water,  the 
stone  strikes  against  the  molecules  of  water  and  sets  them  in 
motion.  The  molecules  which  are  set  in  motion  by  the  stone 
strike  against  those  next  to  them ;  these  in  turn  hit  the  next 
set,  and  a  wave  runs  out  in  the  water.  When  a  bell  is  rung, 
the  bell  vibrates  and  strikes  the  air  molecules  next  to  it,  set- 
ting them  in  motion.  These  strike  the  next  molecules,  and 
so  on,  and  a  wave  runs  out  through  the  air.  When  these  air 
waves  strike  the  ear,  they  start  impulses  in  the  auditory  nerve, 
the  impulses  are  carried  to  the  brain,  and  we  hear  the  bell  ring. 
Big  air  waves  cause  loud  sounds,  and  small  waves  cause  slight 
sounds.  Great  sound  waves  may  strike  the  ear  with  such  force 
as  to  break  the  tympanic  membrane  (Fig.  119),  and  they  may 
also  break  windows  and  jar  houses. 

The  Ear.  The  ear  is  an  organ  so  constructed  that  when 
the  sound  waves  strike  it,  the  afferent  nerves  in  it  will  be 

stimulated.  It  is  divided  into 


TEMPORAL   BONE 


three    parts,  —  the    external, 
middle,  and  internal  ear. 

The  External  Ear.  The  ex- 
ternal ear  includes  the  part 
that  we  see  and  the  canal 
(auditory  canal)  leading  down 
to  the  middle  ear.  The  ex- 
ternal ear  is  composed  of  a 
piece  of  cartilage  covered 
with  skin.  Its  function  is  to 
catch  the  sound  waves  and 
turn  them  down  the  canal  to 
the  middle  ear.  When  animals  are  listening  intently,  they 
hold  up  their  ears  to  catch  as  much  of  the  sound  waves  as 
possible,  and  a  man  sometimes  holds  his  hand  behind  his 


FIG.  119.     The  ear. 


THE  SPECIAL   SENSES 


253 


ear  to  help  in  turning  the  sound  waves  down  the  canal  to  the 
middle  ear. 

The  Middle  Ear.  The  middle  ear  is  a  little  cavity  in  the 
temporal  bone  of  the  skull.  The  cavity  is  shaped  like  a 
drum,  and  is  often  called  the  tympanum,  or  ear  drum.  At 
the  inner  end  of  the  auditory  canal  is  the  tympanic  mem- 
brane. This  stretches  like  a  piece  of  thin  skin  across  the 
bottom  of  the  canal,  and  separates  the  external  ear  from  the 
tympanum.  The  cavity  of  the  tympanum  is  filled  with  air. 

The  Bones  of  the  Ear.  In  the  middle  ear  are  three  very 
small  bones,  —  the  malleus  (hammer),  the  incus  (anvil),  and 
the  stapes  (stirrup).  The  malleus 
is  fastened  to  the  tympanic  mem- 
brane, the  stapes  fits  into  an  open- 
ing that  leads  into  the  internal  ear, 
and  the  incus  is  between  the  mal- 
leus and  the  stapes.  These  three 
bones  stretch  across  the  middle 
ear  from  the  tympanic  membrane 
to  the  inner  wall. 

The  Eustachian  Tube.  The 
Eustachian  tube  is  a  narrow  pas- 
sageway that  leads  from  the  mid- 
dle ear  to  the  pharynx.  It  enters 
the  pharynx  high  up  in  the  side 
wall,  opening  almost  into  the  back  part  of  the  nasal  cham- 
ber. Through  the  Eustachian  tube  the  air  passes  out  of 
and  into  the  middle  ear,  and  keeps  the  pressure  of  the  air 
within  the  tympanum  the  same  as  the  outside  air  pressure. 
If  a  Eustachian  tube  becomes  closed,1  the  varying  pressure 

1  In  colds,  catarrh,  scarlet  fever,  measles,  pneumonia,  and  in  some  other  dis- 
eases, inflammation  may  extend  up  the  Eustachian  tubes  and  cause  deafness 


FIG.  120.     Bones  of  the  ear. 


254 


HUMAN  PHYSIOLOGY 


SEMICIRCULAR, 
CANALS 


NING   FOR   STAPES 


of  the  atmosphere  caused  by  changing  conditions  of  the 
weather  and  by  passing  to  the  lighter  atmospheres  of  higher 
altitudes  or  the  heavier  atmospheres  of  lower  altitudes, 
causes  an  unequal  pressure  on  the  two  sides  of  the  tympanic 
membrane.  This  causes  deafness. 

The  Internal  Ear.     The  internal  ear  lies  deep  in  the  tem- 
poral  bone,  and    is    divided    into   three  parts.     The    central 

part  is  the  vestibule ;  the  front 
part,  which  is  coiled  like  a  snail 
shell,  is  the  cochlea ;  and  the 
back  part  is  the  semicircular 
canals.  The  entire  internal  ear 
is  filled  with  fluid.  Standing 
out  in  this  fluid  from  the 
walls  are  slender,  hair-like  cells, 
that  at  their  inner  ends  are 
connected  with  the  fibers  of 
the  auditory  nerve.  The  im- 
pulses that  cause  us  to  hear 
come  from  the  cochlea. 
How  a  Sound  is  heard.  The  external  ear  catches  the  sound 
wave  and  turns  it  down  the  auditory  canal,  at  the  bot- 
tom of  which  the  wave  strikes  the  tympanic  membrane. 
The  membrane  swings  out  and  in,  and  sets  the  chain  of 
bones  in  motion.  The  malleus  pushes  on  the  incus,  and  the 
incus  on  the  stapes.  The  stapes  is  thus  forced  in  against  the 
fluid  in  the  vestibule  and  in  this  fluid  waves  are  set  up  which 
run  through  the  internal  ear,  striking  against  and  moving  the 
hair-like  cells  that  project  into  the  fluid.  This  starts  im- 

by  closing  the  tubes  (page  270).  "  Adenoid  growths "  are  swellings  in  the 
mucous  membrane  of  the  nasal  chamber.  These  may  push  back  and  close  the 
Eustachian  tube,  thus  causing  deafness. 


FIG.  121.     The  internal  ear.    B  shows 
the  natural  size  of  the  internal  ear. 


THE  SPECIAL  SENSES  255 

pulses  that  travel  up  the  auditory  nerve  to  the  brain,  and 
causes  a  sensation  of  sound. 

Function  of  the  Semicircular  Canals.  The  semicircular 
canals  are  not  concerned  in  hearing,  but  their  function  is  to 
assist  in  retaining  the  equilibrium  of  the  body.  One  canal 
lies  behind  the  vestibule  in  a  vertical  plane,  and  if  the  head 
moves  forward  or  backward  in  the  way  that  it  moves  in  nod- 
ding, the  fluid  in  this  canal  is  set  in  motion.  Another  canal 
runs  outward  from  the  vestibule  in  a  horizontal  plane;  when 
the  head  is  turned  to  the  side,  as  when  one  turns  the  head  to 
look  over  the  shoulder,  the  fluid  in  this  canal  is  set  in  motion. 
The  other  canal  runs  up  and  outward  from  the  vestibule  in 
a  vertical  plane,  so  that  if  the  head  moves  toward  the  side  in 
the  way  it  does  when  it  is  bent  over  toward  the  shoulder,  the 
fluid  in  this  canal  moves. 

If  the  body  leans  in  any  direction,  the  fluid  in  one  or  more 
of  these  canals  is  always  set  in  motion,  and  impulses  are  sent 
to  the  brain,  bringing  information  in  regard  to  the  direction  in 
which  the  body  is  beginning  to  fall.  Impulses  are  then  sent 
out  from  the  brain  that  cause  the  proper  muscles  to  contract 
and  bring  the  body  again  to  the  upright  position.  Sometimes 
the  semicircular  canals  become  diseased,  and  then  there  is 
great  difficulty  in  retaining  the  equilibrium  of  the  body,  be- 
cause it  is  not  noticed  that  the  body  is  beginning  to  fall. 
Sight  and  impulses  from  the  muscles  assist  in  keeping  the 
equilibrium,  but  a  prominent  part  of  this  work  is  done  by  the 
semicircular  canals. 

Care  of  the  Ears.  A  blow  on  the  side  of  the  head  is  danger- 
ous, for  it  may  send  such  a  strong  air  wave  down  the  auditory 
canal  that  the  tympanic  membrane  will  be  ruptured.  Live 
insects  in  the  ear  may  cause  great  distress  by  buzzing  and 
moving  about.  They  can  be  drowned  by  pouring  oil  or  water 


256  HUMAN  PHYSIOLOGY 

into  the  ear.  No  one  but  a  physician  should  attempt  to  re- 
move these  or  other  objects  from  the  ear,1  because  in  doing  so 
there  is  great  danger  that  an  unskilled  person  will  injure  the 
lining  of  the  auditory  canal  or  break  the  tympanic  membrane. 

The  hearing  may  be  injured  by  quinine,  and  this  should  be 
taken  for  any  considerable  time  only  under  the  advice  of  a 
physician.  Earaches  and  deafness  are  caused  by  various 
troubles,  very  often  by  catarrh  that  has  spread  up  the  Eusta- 
chian  tube  and  affected  the  middle  ear.  Earache  may  some- 
times be  prevented  at  night  by  wearing  a  hood  or  nightcap 
while  sleeping,  but  wearing  cotton  in  the  ears  and  pouring 
oil  and  other  liquids  into  them  often  brings  on  serious  trouble, 
and  should  not  be  practiced.  Children  should  not  be  left  to 
outgrow  ear  troubles  or  they  will  often  suffer  great  pain  need- 
lessly, and  perhaps  will  have  the  hearing  permanently  im- 
paired. Among  adults  about  one  third  have  the  hearing 
affected  in  one  or  both  ears  largely  because  of  neglect  in 
youth. 

Summary.  Some  of  the  afferent  nerve  impulses  cause  sen- 
sation. General  sensations  are  produced  by  impulses  that 
arise  within  the  body.  In  the  special  sense  organs  the 
nerves  end  in  such  a  way  that  they  are  stimulated  from  out- 
side the  body.  Seeing,  hearing,  smelling,  tasting,  and  feel- 
ing are  the  special  senses. 

The  afferent  nerves  of  the  skin  end  in  tactile  corpuscles,  at 
the  bases  of  tactile  cells,  and  in  free  nerve  endings.  In  feel- 
ing objects,  stimuli  are  started  in  the  nerves  by  pressure  ; 
and  from  these  stimuli  the  brain  forms  many  judgments  in 

1  The  bitter  wax  in  the  auditory  canal  is  secreted  by  small  glands  in  the  skin. 
It  is  a  protection  against  insects.  Scraping  the  wax  out  of  the  ears  with  the  head 
of  a  pin  or  other  piece  of  metal  may  cause  the  lining  of  the  auditory  canal  to  be- 
come inflamed,  and  greatly  increase  the  quantity  of  wax  secreted, 


THE  SPECIAL  SENSES  257 

regard  to  the  things  that  we  touch.  In  the  skin  are  nerves 
of  touch,  heat,  and  cold,  and  possibly  nerves  of  pain.  The 
sense  of  touch  is  acute  in  the  tip  of  the  tongue,  lips,  and  fin- 
ger tips,  and  much  less  acute  in  some  other  parts  of  the  body. 

Many  of  the  fibers  of  the  nerves  of  taste  end  free  in  the 
mucous  membrane  of  the  tongue  and  of  the  back  part  of  the 
mouth.  Other  fibers  end  in  taste  buds.  Before  anything 
can  be  tasted  it  must  be  dissolved. 

The  olfactory  cells  are  nerve  cells  in  the  nasal  mucous 
membrane.  Impulses  are  started  in  these  cells  by  odors. 
The  olfactory  cells  are  delicate  nerve  cells,  and  if  they  are 
destroyed,  the  sense  of  smell  is  permanently  lost. 

A  sound  wave  is  produced  by  setting  in  motion  the  mole- 
cules of  the  air.  When  these  waves  strike  the  ear,  they 
cause  us  to  hear. 

The  ear  is  composed  of  the  external,  internal,  and  middle 
ear.  The  external  and  middle  ears  are  separated  by  the 
tympanic  membrane.  The  middle  ear  contains  the  malleus, 
incus,  and  stapes.  The  Eustachian  tube  puts  the  air  in  the 
middle  ear  into  communication  with  the  outside  air.  The 
internal  ear  is  composed  of  the  vestibule,  cochlea,  and  semi- 
circular canals.  The  canals  assist  in  preserving  the  equilib- 
rium of  the  body. 

When  a  sound  wave  strikes  the  external  ear,  it  is  turned 
down  the  auditory  canal  and  sets  in  motion  the  tympanic 
membrane.  This  moves  the  chain  of  bones  in  the  middle 
ear,  and  they  set  up  waves  in  the  fluid  in  the  internal  ear. 
These  waves  start  impulses  in  the  nerves  of  hearing  that 
are  carried  to  the  brain,  and  cause  sensations  of  sound.  The 
ear  should  have  intelligent  care,  for  many  cases  of  defective 
hearing  come  from  neglecting  ear  troubles  in  children. 


253  HUMAN  PHYSIOLOGY 


QUESTIONS 

What  causes  sensations?  Name  some  of  the  general  sensations. 
Where  do  the  nerve  impulses  that  cause  these  sensations  originate? 
Name  the  special  sense  organs.  How  are  the  nerve  endings  in  each 
one  stimulated? 

Give  three  ways  in  which  the  afferent  nerves  end  in  the  skin. 
How  are  impulses  started  in  these  nerves  when  we  touch  an  object? 
Explain  how  we  are  able  to  judge  of  certain  properties  of  objects  by 
touching  them.  What  different  kinds  of  nerves  end  in  the  skin? 
Where  is  the  sense  of  feeling  acute?  Where  is  it  least  acute? 

Give  two  ways  in  which  the  nerves  of  taste  end  in  the  tongue. 
Describe  a  taste  bud.  How  is  the  nerve  of  taste  stimulated?  Does 
a  chicken  taste  corn  when  it  eats  it  ? 

Where  is  the  organ  of  smell  located?  Describe  the  olfactory  cells. 
What  kind  of  cells  are  they?  What  is  an  odor?  How  are  impulses 
started  in  the  olfactory  cells?  In  what  ways  may  these  cells  be  injured  ? 

Of  what  is  air  composed?  Explain  how  a  bell  starts  waves  in  the 
air.  How  do  these  waves  cause  the  sensation  of  sound  ? 

Name  the  three  divisions  of  the  ear.  What  is  the  function  of  the 
external  ear?  What  is  the  middle  ear  called?  Why?  What  and 
where  is  the  tympanic  membrane?  Name  the  bones  of  the  ear. 
Where  are  the  Eustachian  tubes?  What  is  their  use? 

Name  the  parts  of  the  internal  ear.  With  what  is  it  filled  ?  Ex- 
plain how  a  stimulus  is  started  in  the  auditory  nerve.  What  is  the 
function  of  the  semicircular  canals?  How  are  the  impulses  started 
in  the  nerves  that  are  connected  with  these  canals?  When  one  whirls 
himself  rapidly  about  and  then  stops,  what  causes  him  to  have  a  sen- 
sation of  dizziness? 

How  may  a  blow  on  the  ear  injure  the  hearing?  How  may  an 
insect  in  the  ear  be  killed?  What  is  a  common  cause  of  earache  and 
deafness?  Why  should  ear,  troubles  in  children  receive  attention? 


CHAPTER    XX 

THE   SPECIAL   SENSES   (Continued):    SEEING 

ALL  space  is  filled  with  an  invisible  substance  called  ether, 
and  light  is  waves  in  the  ether.  The  eye  is  so  constructed 
that  when  the  ether  waves  enter  it,  they  stimulate  the  affer- 
ent nerves  and  start  impulses  to  the  brain  that  cause  the 
sensation  of  sight. 

Protection  of  the  Eyes.  The  eyes  are  very  important  and 
very  delicate  organs,  and  must  therefore  be  well  protected. 
The  deep  bony  eyesockets  are  a  great  protection  from  blows. 
The  inside  of  the  eyesocket  is  lined  with  a  layer  of  fat  which 
forms  a  soft  cushion  for  the  eyes  to  rest  and  turn  on,  and  if 
the  eye  is  struck,  the  fatty  layer  between  it  and  the  bone 
assists  in  preventing  injury. 

The  eyelids,  eyelashes,  and  eyebrows  also  assist  in  protect- 
ing the  eyes.  The  eyelids  screen  them  from  dust  and  light, 
and  close  if  a  blow  is  threatened.  The  eyelashes  guard  the 
eyes  from  dust  and  light,  and  the  eyebrows  keep  the  sweat 
from  running  down  from  the  forehead  into  the  eyes. 

The  Lachrymal  Glands.  In  the  outer  corner  of  each  upper 
eyelid  is  located  a  lacJirymal gland,  very  similar  in  structure  to 
a  small  salivary  gland.  These  glands  secrete  the  tears  and 
pour  them  into  the  eyes  at  the  upper  outer  corners.  The  tears 
flow  down  across  the  eye  to  the  inner  corner,  where  they  enter 
the  lachrymal  duct,  which  carries  them  down  into  the  nasal 
chamber.  In  their  passage  across  the  eyes,  the  tears  cleanse 

259 


260 


HUMAN-  PHYSIOLOGY 


FIG.  122. 


The  lachrymal  gland  and 
duct. 


the  eye,  washing  away  dust  and  germs.     The  workings  of  the 
lachrymal  glands  give  us  another  illustration  of  the  effect  of 

the  mind  on  the  body ;  for 
sorrow,  pain,  and  sometimes 
anger  cause  them  to  secrete  so 
abundantly  that  the  tears  cannot 
all  be  carried  away  by  the  lach- 
rymal ducts,  but  overflow  on  the 
cheeks. 

The  Meibomian  Glands.  In 
the  eyelids  are  small  glands 
called  the  Meibomian  glands. 
They  are  very  similar  to  sebaceous  glands,  and  empty  out 
an  oily  secretion  along  the  edges  of  the  eyelids.  Water 
does  not  flow  freely  over  an  oiled  surface,  and  the  secretion 
from  the  Meibomian  glands  prevents  the  tears  from  over- 
flowing the  eyelids.  When  the 
eyelids  are  inflamed  and  con- 
gested, the  Meibomian  glands 
sometimes  become  diseased, 
and  the  secretion  from  them 
dries  around  the  roots  of  the 
eyelashes,  forming  scales  very 
similar  to  dandruff. 

The  Muscles  of  the  Eyes. 
There  are  six  muscles  to  move 
each  eye.  The  back  ends  of 
these  muscles  are  attached  to  the  walls  of  the  eyesocket.  The 
front  ends  are  attached  to  the  ball  of  the  eye.  By  these 
muscles,  the  eyes  can  be  turned  in  any  direction,  so  that  it  is 
not  always  necessary  to  turn  the  head  toward  the  object  at 
which  we  are  looking. 


FlG.  123.     The  muscles  of  the  eye. 


SEEING  26l 

The  Structure  of  the  Eye.  The  eye  has  three  coats.  The 
outer  one  is  the  sclerotic  coat,  the  middle  one  is  the  choroid 
coat,  and  in  the  back  part  of  the  eye  is  a  third  inner  coat 
called  the  retina.  The  optic  nerve  enters  the  eye  at  the  back 
and  spreads  out  in  the  retina. 


ROTIC  COAT 
CHOROID  COAT 


FlG.  124.     A  diagram  of  a  section  of  the  eye. 

The  interior  of  the  eye  is  divided  by  the  lens  and  the 
ligaments  that  support  the  lens  into  a  small  anterior  cham- 
ber and  a  larger  posterior  chamber.  The  posterior  chamber 
is  filled  with  a  transparent,  jelly-like  substance,  called  the 
vitreous  humor.  The  small  anterior  chamber  is  filled  with 
the  aqueous  humor,  a  watery  fluid  similar  to  tears. 

The  Sclerotic  Coat.  The  sclerotic  coat,  or  white  of  the 
eye,  is  composed  of  dense,  closely  woven  connective  tissue. 
It  has  a  white  color,  except  in  front,  where  it  is  transparent. 
This  transparent  part  is  called  the  cornea,  and  through  it  the 


262  HUMAN  PHYSIOLOGY 

light    passes    into   the  interior  of  the  eye,   as   light   passes 
through  a  window  into  a  house. 

The  Choroid  Coat  and  the  Iris.  The  choroid  coat  is  a  loose 
connective  tissue  coat.  It  contains  pigment  that  gives  it  a 
rich,  dark  color  similar  to  the  inside  of  a  grape  skin.  The 
front  part  of  the  choroid  is  called  the  iris.  This  contains  a 
circular  opening,  the  pupil,  in  its  center.  The  iris  lies  behind 
the  transparent  cornea,  and  being  seen  through  the  cornea, 
gives  the  color  to  the  eye.  A  person  is  black-eyed,  brown- 
eyed,  or  blue-eyed,  according  to  the  pigment  in  his  iris. 

The  Function  of  the  Iris.  The  function  of  the  iris  is  to 
regulate  the  amount  of  light  that  enters  the  eye.  In  the  iris 

are  circular  muscle  fibers,  run- 
ning around  the  pupil,  and 
when  these  contract,  they 
make  the  pupil  smaller. 
Other  muscle  fibers  run  in 
from  the  outer  edge  of  the 
iris  to  the  pupil,  and  when 
FIG.  125.  One  cat  has  been  in  the  dark;  these  contract,  they  enlarge 

the  other  has  been  in  the  light.  ., 

the  pupil. 

The  control  of  the  size  of  the  pupil  is  carried  on  by  invol- 
untary reflexes.  When  a  strong  light  enters  the  eye,  the 
circular  fibers  in  the  iris  contract  and  diminish  the  size  of  the 
pupil.  When  the  light  is  weak,  the  pupil  is  enlarged  and 
more  light  is  admitted  to  the  eye.  When  you  step  out  of  a 
brightly  lighted  room  into  the  dark,  you  cannot  see,  because 
the  pupil  is  too  small  to  allow  enough  light  to  enter.  But  if 
you  remain  out  in  the  dark,  the  pupil  will  be  enlarged  and 
admit  more  light,  and  your  vision  will  become  better.  When 
you  step  from  a  darkened  room  out  into  the  bright  sunshine, 
the  light  dazzles  the  eyes,  because  the  opening  in  the  pupil 


SEEING  263 

is  too  wide  and  lets  in  too  much  light.  After  a  few  minutes, 
the  muscles  of  the  iris  contract  and  diminish  the  size  of  the 
pupil,  thus  adapting  the  eye  to  the  bright  light. 

The  eye  of  a  cat  shows  very  distinctly  the  changes  in  the 
size  of  the  pupil.  In  the  dark  the  pupil  is  large  and  round, 
and  in  a  bright  light  it  is  narrowed  to  a  slit.  This  you  can 
easily  see  for  yourself  by  examining  the  eye  of  a  cat  that  has 
been  in  the  light,  and  then  shutting  the  cat  in  a  dark  room 
or  closet  and  examining  its  eye  again. 

Owls  have  very  large  pupils,  which  enable  them  to  see  at 
night  better  than  most  animals  and  birds;  but  in  a  bright 
light  the  pupil  of  an  owl's  eye  cannot  be  made  small  enough 
to  keep  the  eye  from  being  dazzled  by  the  light.  Many 
animals  (the  cat  and  the  horse  are  examples)  can  see  at  night 
better  than  man  can  see,  because  the  pupils  can  be  opened 
wider  than  can  the  pupil  of  the  human  eye. 

The  Lens.  The  lens  (Fig.  129)  lies  close  against  the  back 
of  the  iris.  It  is  thin  at  the  edges  and  thicker  in  the 
middle,  and  is  composed  of  a  clear,  jelly-like  substance. 
The  lens  is  inclosed  in  a  circular  sac,  and  both  the  sac 
and  the  material  in  it  are  transparent,  so  that  the  light 
can  pass  through  them  to  the  retina  in  the  back  of  the 
eye.  The  lens  is  attached  to  the  choroid  coat  by  the  suspen- 
sory ligament,  which  runs  out  all  around  from  the  outer  edge 
of  the  lens.  Figure  124  shows  the  lens  and  the  suspensory 
ligament  as  they  appear  when  cut  across,  but  you  must 
understand  that  the  lens  is  circular  like  a  coin,  and  that  the 
suspensory  ligament  is  a  ring  with  the  lens  fitted  into  the 
opening  of  the  ring. 

The  Function  of  the  Lens.  The  function  of  the  lens  is  to 
form  images  of  the  objects  that  we  see,  and  to  accommodate  the 
eye  to  near  and  distant  objects.  In  forming  images  in  the 


264  HUMAN  PHYSIOLOGY 

eye,  the  lens  is  assisted  by  the  curved  surface  of  the  cornea. 
On  the  ground  glass  in  the  back  of  a  camera,  you  can  see 
an  image  formed  by  the  lens  in  the  front  of  the  camera. 
The  lens  and  cornea  of  the  eye  form  images  on  the  retina 
in  the  same  way  that  the  image  on  the  camera  is  formed. 

How  a  Lens  forms  an  Image.  Hold  a  convex  lens l  so  that 
sunlight  will  pass  through  it.  You  will  find  that  the  lens 
brings  the  rays  of  light  to  a  focus,  —  that  is,  it  bends  them  so 
that  they  all  meet  in  one  point.  It  does  this  by  changing  the 


FlG.  126.     Image  formed  by  a  convex  lens. 

directions  in  which  the  light  waves  are  running,  causing 
them  all  to  run  toward  one  point.  The  lens  of  the  eye 
bends  all  the  rays  of  light  that  come  from  one  point,  so  that 
they  meet  in  one  point  on  the  retina  of  the  eye.  In  Figure  126 
you  can  see  how  all  the  rays  of  light  from  the  point  of  the 
arrow  meet  in  one  place  and  form  -an  image  of  the  arrow 
point.  In  the  same  way,  an  image  of  the  other  end  of  the 
arrow  is  formed,  and  of  every  other  point  in  the  arrow,  and 
all  these  points  together  make  an  image  of  the  arrow.  So, 
in  looking  at  a  landscape,  an  image  of  the  whole  landscape 
is  formed  in  the  eye,  all  the  rays  of  light  that  come  from  any 
one  part  of  the  scene  in  front  of  the  eye  meeting  in  one  point 
and  forming  an  image  of  that  point  on  the  retina.  The 

1  This   experiment   can   be  performed  with   the   lens   in   a   pair   of   convex 
spectacles. 


SEEING 


265 


images  that  are  formed  in  the  eye,   like    the  images   in  a 
camera,  are  upside  down,  and  the  right 
and  left  sides  are  reversed. 

The  Retina.  The  retina  contains  slen- 
der, pointed  cells  that  are  affected  by 
light.  These  cells  are  connected  with 
the  optic  nerve,  and  when  light  strikes 
the  retina  an  impulse  is  started  which 
passes  back  through  the  optic  nerve  to 
the  brain. 

The  Function  of  the  Brain  in  seeing. 
Impulses  are  started  in  the  eye  by  the 
images  that  fall  on  the  retina,  but  these 
impulses  must  be  carried  to  the  brain  be- 
fore the  sensation  of  sight  is  produced. 
From  the  impulses  that  come  into  the 
brain  from  the  eye,  we  form  judgments 
in  regard  to  the  form,  size,  color,  and 
smoothness  or  roughness  of  objects. 

J  FIG.    127.      When    light 

From  these  impulses  we  can  judge  also  strikesthe  retina,  impulses 

Of     the    distance    Of     Objects     from     US,  Of    are  started  in  the  long,  slen- 
,  ,  ...  i         f      . ,  der  cells  (a  and  b}  of  the 

their    relative    positions,    and    of    their  retina    ^  are;carried 

movements.       That     the     mind     does     not    to  the  brain,  and  cause  the 

always    form    correct    judgments     from   sensation  of  sight, 
the  impulses  that  come  from  the  eye,  you  can  easily  dem- 
onstrate by  looking  at  the  two  lines 
N.  /    of  the  same  length  in  Figure  128. 

y  ~"x.          The    Accommodation    of    the    Eye. 

.  .  The    shape    of    the    lens    must    be 

Z_ -^          changed    according   to    the   distance 

\  /  from  the  eye  of  the  object  that  we 

FIG.  128.  are  looking  at.     When  the  object  is 


266 


HUMAN  PHYSIOLOGY 


close  to  the  eye,  the  lens  must  be 
made  more  convex;  for  a  distant 
object  the  lens  needs  to  be  flat- 
tened. This  change  in  shape  of 
the  lens  is  called  the  accommoda- 
tion of  the  eye  and  is  brought 
about  by  the  ciliary  muscles. 

How  the  Eye  is  accommodated. 
The  suspensory^  ligament  is  at- 
tached to  the  choroid  coat  as  is 
shown  in  Figure  129.  The  front 
ends  of  the  ciliary  muscles  are 
attached  to  the  sclerotic  coat. 
Their  other  ends  are  attached  to 
the  choroid  coat.  When  these 
muscles  contract,  they  stretch  the 
choroid  and  draw  it  forward. 
This  loosens  the  suspensory  liga- 
ment, and  the  lens  of  itself  rounds 
out  and  becomes  more  convex, 
cies  contract  they  draw  forward  the  when  the  ciliary  muscles  relax, 

choroid  coat,  loosen  the  suspensory 

ligament,  and  allow  the  lens  to  be-  the  stretched  choroid  returns  to  its 
come  more  convex.  former    position,    thus    tightening 

the  ligament  again  and  flattening  the  lens. 

The  change  in  shape  of  the  lens  can  be  illustrated  with  a 
small  sac,  or  with  the  swimming  bladder  of  a  fish,  filled  with 
air  or  water.  Pull  on  the  ends  of  the  sac,  and  you  will  flatten 
it.  Decrease  the  pull,  and  of  itself  the  sac  will  round  up,  as 
does  the  lens  when  the  ligament  is  loosened  by  the  choroid's 
coming  forward.  You  should  take  especial  care  to  note 
that  the  contraction  of  the  ciliary  muscles  loosens  the 
ligament,  and  does  not  tighten  it,  for  pupils  who  are 


CILIARY 
MUSCLES 


FIG.  129.    When  the  ciliary  mus- 


SEEING 


267 


studying  the  eye  often  get  an  incorrect  idea  in  regard  to  this 
point. 

Near  sightedness.  The  image  in  the  eye  must  fall  exactly  on 
the  retina,  or  vision  cannot  be  distinct.  In  some  persons,  the 
eyes  are  long  from  the  front 
to  the  back.  In  such  persons, 
the  rays  of  light  meet  before 
they  reach  the  retina.  This 
makes  an  indistinct  image,  as 
does  a  camera,  microscope,  or 
field  glass,  when  it  is  out  of 
focus.  In  B  ( Fig.  1 30)  you  can 
see  how  the  rays  of  light  from 
the  head  of  the  arrow  meet  in 
front  of  the  retina,  and  how, 
when  they  reach  the  retina, 
they  have  crossed  and  sepa- 
rated again,  scattering  the 
image  on  the  retina  instead  of 
making  it  clear  and  distinct  at 
one  point.  In  such  an  eye, 
the  images  of  the  different 
points  overlap,  and  a  blurred, 
indistinct  image  of  the  whole  object  is  the  result.  Near- 
sighted persons  usually  have  prominent  eyes,  and  the  cornea 
usually  is  more  convex  than  it  is  in  the  normal  eye. 

Far-sightedness.  A  far-sighted  eye  is  too  short  from  front 
to  back.  In  such  an  eye,  the  retina  is  so  close  to  the  lens 
that  the  rays  of  light  have  not  been  brought  together  when 
they  get  to  it,  and  the  image  is  blurred  (Fig.  130  C).  Per- 
sons with  eyes  of  this  kind  see  distant  objects  best,  because 
the  rays  from  these  objects  meet  more  quickly  than  do  those 


FIG.  130.  A,   normal;   B,  near-sighted; 
and  C,  far-sighted  eye. 


268  HUMAN  PHYSIOLOGY 

from  near  objects.  In  a  far-sighted  eye,  the  cornea  is  usually 
flatter  than  it  is  in  the  normal  eye,  and  in  far-sighted  per- 
sons the  eyes  are  not  so  prominent  as  they  are  in  near-sighted 
persons. 

Astigmatism.  In  astigmatism,  the  curvature  of  the  cornea 
is  uneven,  some  parts  being  flatter  than  other  parts.  The 
rays  of  light  that  pass  through  the  flatter  places  on  the 
cornea  are  not  brought  to  a  focus  as  soon  as  the  rays  passing 
through  the  more  convex  parts.  A  distinct  image  cannot  be 
formed  in  such  an  eye,  for  the  lens  cannot  be  so  shaped  that 
all  the  rays  from  one  point  will  come  together  in  a  single 
point  on  the  retina. 

Eyes  of  Old  Persons.  In  old  persons,  the  material  of  which 
the  lens  is  composed  becomes  harder  and  less  fluid,  and  when 
the  suspensory  ligament  is  slackened,  the  lens  fails  to  change 
its  shape.  The  power  of  accommodation  is  thus  lost.  One 
of  the  most  wonderful  things  about  the  eye  is  the  way  it 
accommodates  itself  to  objects  at  different  distances,  and  in 
old  persons  this  power  is  to  a  certain  extent  lost. 

Spectacles.  If  a  sharp,  clear  image  is  not  formed  on  the 
retina,  eye  trouble  is  certain  to  result.  Near-sighted,  far- 
sighted,  and  astigmatic  eyes  need  spectacles  or  eyeglasses 
to  assist  in  forming  distinct  images  on  the  retina.  The  kind 
of  lenses  that  are  needed  in  the  spectacles  depends  on  where 
the  image  falls  in  the  eye,  each  particular  eye  needing  to  be 
fitted  with  a  lens  that  will  cause  the  image  to  fall  exactly  on 
the  retina. 

Concave  lenses  spread  the  rays  of  light  farther  apart.  If  a 
concave  lens  is  placed  before  a  near-sighted  eye,  the  lens  will 
spread  the  rays  of  light  and  cause  them  to  meet  farther  back 
in  the  eye  (Fig.  131).  A  person  who  is  very  near-sighted 
will  need  a  strongly  concave  lens,  and  a  person  who  is  only 


SEEING 


269 


a  little  near-sighted  will  need 
only  a  slightly  concave  lens. 
Each  eye  needs  a  lens  that 
will  bring  the  rays  to  a  focus 
on  the  retina. 

Convex  lenses  bend  tJie  rays 
of  light  together  and  cause 
them  to  meet  more  quickly. 
In  far-sighted  eyes,  the  rays 
have  not  yet  met  when  they 
reach  the  retina,  and  by  plac- 
ing a  convex  lens  before  such 
an  eye,  the  rays  can  be 
brought  together  and  made 


FlG.  131.     How  glasses  cause  the  rays 
of  light  to  meet  on  the  retina. 


to  meet  on  the  retina. 
In  astigmatic  eyes,  the  lens  must  be  ground  to  suit  the  eye. 
Where  there  is  a  little  hill  on  the  cornea,  a  concave  place 
must  be  ground  out  in  the  lens,  and  where  there  is  a  flat 
place  on  the  cornea,  the  lens  must  be  convex.  Old  persons 
need  one  pair  of  glasses  for  seeing  distant  objects,  and  another 
pair  for  seeing  near  objects. 


HYGIENE   OF  THE   EYES 

It  is  a  great  mistake  to  think  of  the -eye  as  a  separate  part 
of  the  body,  doing  its  work  without  connection  with  the  other 
body  parts.  Like  all  the  other  organs,  it  is  intimately  related 
to  the  rest  of  the  body,  and  any  defect  or  trouble  in  the  eye 
is  likely  to  affect  other  organs,  the  nervous  system,  and  the 
general  health.  It  is,  therefore,  important  to  care  for  the  eyes, 
not  only  to  relieve  pain  in  the  eyes  themselves  and  to  have 
good  vision,  but  for  the  purpose  of  keeping  the  entire  body  in 
health. 


2/0  HUMAN  PHYSIOLOGY 

Care  of  the  Eyes.  Spectacles  or  eyeglasses  sJiould  be  worn 
when  they  are  needed.  In  securing  thesej  one  should  always 
go  to  a  reliable  physician  or  oculist,  and  not  to  some  unskilled 
person  or  traveling  optician,  for  it  requires  considerable  skill 
and  care  to  examine  an  eye,  and  to  tell  exactly  the  kind  of 
lens  that  is  suited  to  it.  Also,  the  eye  sometimes  changes 
very  rapidly,  so  that  the  lenses  of  the  spectacles  need  to  be 
changed,  and  it  is  always  better  to  deal  with  some  one  who 
can  examine  the  eyes  from  time  to  time,  and  change  the 
lenses  as  changes  are  needed. 

The  importance  of  having  the  eyes  properly  fitted  with 
glasses  cannot  be  too  strongly  insisted  on,  for  many  cases  of 
nervousness,  headache,  indigestion,  nausea,  and  mental  dull- 
ness vanish  as  if  by  magic  when  glasses  are  adjusted  to  the 
eyes.1  If  a  person  has  any  signs  of  eye  trouble,  or  if  he  has 
headaches  and  stomach  trouble  for  which  there  seems  to  be 
no  reason,  the  eyes  should  be  examined  at  once. 

A  good  HgJit  sJiould  always  be  used  in  reading  or  in  doing 
other  close  work.  To  read  by  a  dim  light,  as  when  one  reads 
on  into  the  twilight,  is  exceedingly  injurious.  A  dazzling, 
bright  light  is  also  injurious,  especially  if  it  shines  directly 
into  the  eye.  In  reading,  one  should  sit  so  that  the  light  will 

1  To  THE  TEACHER  :  A  considerable  proportion  of  the  children  who  are  re- 
garded as  dull  in  school  fall  behind  their  classes  because  of  defective  hearing  or 
vision.  The  teacher  should  carefully  watch  his  dull  pupils  for  symptoms  of 
trouble  in  the  nasal  passages,  test  the  hearing  by  some  such  device  as  trying  how 
far  the  child  can  hear  the  ticking  of  a  watch,  and  note  if  the  child  holds  his 
book  close  to  his  eyes  or  shows  other  symptoms  of  eye  trouble.  The  attention 
of  parents  should  be  called  to  any  defects  that  may  be  discovered,  and  the  parents 
should  be  made  to  understand  the  importance  of  medical  attention  for  such 
cases.  Any  close  work  is  injurious  to  the  eyes  of  young  children,  and  kinder- 
garten teachers  especially  should  take  care  to  see  that  the  eyes  of  the  children 
in  their  charge  are  not  injured  by  too  much  sewing,  weaving,  or  other  similar 
work.  (See  also  page  308,  note  I.) 


SEEING  271 

fall  on  the  book,  but  not  into  the  eyes.  Facing  a  window  in 
the  daytime  is  injurious, and  it  is  also  injurious  to  read  on  a 
dark  day  in  a  corner  of  a  room  far  from  a  window. 

Reading' while  lying  down  is  a  bad  practice ;  because  in  this 
position,  too  great  a  blood  supply  comes  to  the  eyes,  and  they 
become  congested  with  blood.  Then,  too,  the  book  or  paper 
is  often  held  in  a  very  awkward  position,  which  strains  the 
eyes. 

Resting  the  eyes  occasionally  is  very  helpful.  In  reading, 
the  eye  is  accommodated  for  near  objects,  and  the  ciliary 
muscles  must  be  held  contracted  to  round  up  the  lens.  In 
reading  for  long  periods  of  time,  these  muscles  become  ex- 
hausted. It  is,  therefore,  a  good  idea  to  stop  occasionally 
while  reading,  and  to  close  the  eyes  or  look  out  of  a  window 
at  a  distant  object,  allowing  the  ciliary  muscles  to  relax  and 
rest.  This  advice  applies  of  course  when  one  is  doing  any 
work  that  is  hard  on  the  eyes. 

Dust  is  exceedingly  injurious  to  the  eyes.  It  always  causes 
irritation  by  scratching  the  surface  of  the  eye  and  the  lining 
of  the  eyelids,  and  it  carries  into  the  eye  germs  that  may 
cause  inflammation.  For  congestion  and  redness  of  the 
eyes,  bathing  in  cold  water  is  helpful.  A  little  boracic  acid 
dissolved  in  water  (the  exact  strength  of  the  solution  is  not 
important)  and  dropped  into  the  eyes  at  night  on  retiring 
has  a  very  soothing  effect  on  the  eyes,  and  helps  to  kill 
germs  that  get  into  them.  But  in  any  serious  or  long-con- 
tinued trouble  with  the  eyes,  a  physician  or  oculist  should 
always  be  consulted. 

Effect  of  Tobacco  and  Alcohol  on  the  Eyes.  In  a  few  per- 
sons, tobacco  affects  the  nerves  of  sight  so  that  distinct  vision 
and  the  power  of  distinguishing  between  colors  are  lost. 
Tobacco  smoke  is  irritating  to  the  eyes,  and  in  a  considerable 


HUMAN"  PHYSIOLOGY 

number  of  persons,  smoking  brings  on  a  congestion  and  red- 
ness of  the  eyes  and  eyelids.  Alcohol  congests  the  vessels 
of  the  eyes,  as  it  does  those  of  other  parts  of  the  body,  but 
the  effects  of  alcohol  and  tobacco  on  the  eyes  in*  most  cases 
are  not  very  serious,  as  compared  with  their  effects  on  some 
of  the  other  organs  of  the  body. 

Summary.  The  eye  is  protected  by  the  eyesocket,  the  eye- 
lids, eyelashes,  and  eyebrows.  It  is  cleansed  by  tears  that  are 
secreted  by  the  lachrymal  gland  and  are  drained  off  into  the 
nose  by  the  lachrymal  duct.  The  edges  of  the  eyelids  are 
kept  oiled  by  the  Meibomian  glands  so  that  the  tears  will 
not  overflow  on  the  cheeks. 

The  eye  is  moved  by  six  muscles.  It  has  three  coats,  — 
the  sclerotic  coat,  choroid  coat,  and  retina.  Its  interior  is 
divided  by  the  lens  and  the  suspensory  ligament  into  an  ante- 
rior and  a  posterior  chamber.  The  anterior  chamber  contains 
the  aqueous  humor ;  the  posterior  chamber  contains  the  vitre- 
ous humor. 

The  transparent  front  portion  of  the  sclerotic  coat  is  called 
the  cornea,  and  the  front  portion  of  the  choroid  coat  is  the 
iris.  The  iris  gives  the  color  to  the  eye.  In  the  center  of 
the  iris  is  an  opening  called  the  pupil.  The  muscles  in  the 
iris  open  and  close  the  pupil  and  in  this  way  regulate  the 
amount  of  light  that  enters  the  eye. 

The  lens  and  cornea  form  images  on  the  retina  of  the  eye. 
The  images  start  impulses  to  the  brain  that  give  us  the  sensa- 
tion of  sight.  The  eye  is  accommodated  for  near  and  far 
objects  by  changing  the  shape  of  the  lens. 

It  is  essential  to  clear  vision  that  the  image  fall  on  the 
retina.  Eye  troubles  cause  headaches  and  a  derangement  of 
the  digestive  and  nervous  systems.  When  spectacles  are 
needed,  they  should  be  worn.  A  good  light  should  be  used 


SEEING  273 

in  reading,  and  occasionally  the  eyes  should  be  rested.  Dust 
is  harmful  to  the  eyes  and  tobacco  and  alcohol  may  in- 
juriously affect  them. 

QUESTIONS 

What  is  light  ?     What  does  light  do  when  it  enters  the  eye  ? 

How  is  the  eye  protected?  Where  are  the  lachrymal  glands? 
the  lachrymal  ducts?  the  Meibomian  glands?  What  is  the  function 
of  the  Meibomian  glands? 

How  many  muscles  move  each  eye?  Where  are  these  muscles 
attached?  Name  the  coats  of  the  eye;  the  two  chambers  of  the 
eye.  What  separates  the  two  chambers?  Where  is  the  vitreous 
humor?  the  aqueous  humor? 

Of  what  is  the  sclerotic  coat  of  the  eye  composed?  What  does 
the  choroid  coat  contain?  What  is  the  cornea?  iris?  pupil? 
What  is  the  function  of  the  iris?  How  is  the  size  of  the  pupil 
changed?  Under  what  conditions  does  it  enlarge  and  contract? 

Describe  the  lens.  How  is  it  held  in  place?  What  is  its  func- 
tion? Explain  how  an  image  is  formed  by  a  lens.  Describe  the 
cells  in  the  retina  and  tell  how  nerve  impulses  from  these  cells 
reach  the  brain.  What  part  has  the  brain  in  seeing? 

Where  are  the  ciliary  muscles  attached  ?  Explain  how  the  eye  is 
accommodated. 

What  is  the  trouble  in  a  near-sighted  eye?  in  a  far-sighted  eye? 
in  an  astigmatic  eye  ?  in  the  eyes  of  old  persons  ? 

What  effect  have  concave  lenses  on  light  waves  that  pass  through 
them  ?  convex  lenses  ?  What  kind  of  lenses  are  needed  in  specta- 
cles for  near-sighted  eyes?  for  far-sighted  eyes?  for  astigmatic 
eyes? 

What  are  some  of  the  ailments  brought  on  by  eye  trouble  ?  Why 
is  it  important  to  wear  spectacles  when  they  are  needed?  From 
whom  should  they  be  procured  ?  Mention  three  points  that  should 
be  kept  in  mind  in  caring  for  the  eyes.  Why  is  dust  injurious  to 
the  eyes?  What  effect  has  tobacco  on  the  eyes?  alcohol? 


CHAPTER   XXI 

ACCIDENTS 

IN  cases  of  accidents  and  emergencies  it  is  often  very  im- 
portant that  something  be  done  at  once.  Some  of  the  best 
measures  to  be  employed  in  such  cases  will  be  discussed  in 
this  chapter.  When  the  time  comes  for  putting  these  measures 
into  use,  a  cool  head  and  quick  action  are  absolutely  neces- 
sary. Therefore,  at  such  times,  keep  cool,  think  quickly,  and 
act  sensibly  and  at  once. 

How  to  keep  Afloat  in  Water.  It  requires  very  little  force 
to  keep  the  human  body  afloat  in  water.  In  trying  to  keep 
afloat,  therefore,  keep  your  body  low  in  tJie  water.  A  small 
board  is  enough  to  keep  you  afloat  if  you  will  do  this.  If 
thrown  into  the  water  by  the  upsetting  of  a  small  boat,  do 
not  try  to  climb  upon  the  boat,  or  you  may  sink  it.  Keep 
your  body  low  in  the  water  and  support  yourself  by  taking 
hold  of  the  boat  with  your  hand.  If  you  break  through  the 
ice,  keep  your  body  low  in  the  water 
and  take  hold  of  the  edge  of  the  ice 
with  your  hand.  Every  one  sJiould  learn 
to  swim,  for  knowing  how  to  swim 
even  a  few  yards  will  often  save  life. 

How   to   revive   a   Person  who   has 
FIG.  132.     Draining    the     been  under  Water.     In  drowning,  the 
trouble  is  that  the  air  is  cut  off  from 

the  lungs  by  the  water.     The  great  point,  therefore,  is  to  get 
air  into  the  lungs  as  quickly  as  possible. 

274 


ACCIDENTS 


2/5 


The  first  thing  is  to  drain  the  water  from  the  lungs.  Turn 
the  patient  on  his  face  and  lift  him  as  is  shown  in  Figure  132. 
Lift  him  up  two  or  three  times,  jerking  the  body,  so  that  all 
the  water  will  come  out  of  the  lungs.  Do  this  quickly  (in 
about  thirty  seconds). 

After  the  water  is  out  of  the  lungs,  turn  the  patient  on 
his  back.  Put  something  —  a  pillow,  clothes,  anything  at 
hand  —  under  the  shoulders  to  throw  the  chest  out.  Loosen 
the  clothing  at  the  neck  and  waist.  The 
tongue  must  be  drawn  out  of  the  mouth  and 
either  held  or  fastened  by 
having  a  pin  thrust  through 
the  tip.  Otherwise  it  will 
drop  back  and  close  the 
throat.  All  this  must  be 
done  quickly,  for  life  often 
depends  on  starting  respi- 
ration at  once. 

The  next  step  is  to  start 
artificial  respiration.  To 
do  this,  grasp  the  patient's 
arms  and  pull  them  up  far 
over  his  head  (Fig.  133) 
while  you  count  one,  two, 
three.  Then  bring  the 

arms  down  to  the  sides  and     FIG.  133.    Artificial  respiration  carried  on  by 

press  as  hard  as  possible  one  person< 

on  the  sides  of  the  chest  to  force  the  air  out  of  the  lungs. 
Do  this  about  twelve  or  fifteen  times  a  minute.  If  the 
patient  does  not  begin  to  breathe  in  three  or  four  minutes, 
turn  him  over  and  try  if  any  more  water  can  be  drained  from 
the  lungs. 


276 


HUMAN  PHYSIOLOGY 


When  there  are  two  persons  to  care  for  the  patient,  they 
should  take  the  positions  shown  in  Figure  134,  and  when 

the  arms  are  brought 
down  to  the  sides,  one 
should  press  on  the 
abdomen  and  chest 
in  such  a  way  as  to 
force  in  the  ribs  and 
drive  the  abdominal 
organs  and  diaphragm 
upward.  Keep  up 
artificial  respiration 
for  two  hours,  if 
necessary,  for  per- 

FlG.  134.   Artificial  respiration  carried  on  by  two  persons.  •,'  •        •, 

after   showing    no    signs    of    life   for   this    length   of   time. 

Another  method  is  to  turn  the  patient  on  his  face  and  lift 
him  by  the  clothing  between  the  shoulders,  or  by  catching 
the  fingers  in  the  armpits.  Then  lower  the  body  to  the  ground 
and  force  the  air  out  of  the  lungs  by  pressing  on  the  back 
and  sides.  A  great  advantage  of  this  method  is  that  the 
tongue  needs  no  care. 

Other  treatment  is  useful  when  there  is  help  enough  to  give 
it  without  interfering  with  the  artificial  respiration.  The  limbs 
should  be  rubbed  upward  to  make  the  blood  in  the  veins  flow 
to  the  heart,  and,  if  possible,  the  wet  clothing  should  be  re- 
moved and  the  body  wrapped  in  warm  blankets.  Often  the 
easiest  way  of  warming  the  patient  is  to  pour  warm  water 
over  his  clothing  and  then  cover  him  with  a  blanket.  Hot- 
water  bottles  or  other  warm  objects  will  help  to  keep  up  the 
heat.  In  cold  weather  the  warming  of  the  patient  is  a  very 
important  part  of  the  treatment.  After  the  patient  begins  to 


ACCIDENTS 


277 


breathe,  he  should  be  kept  warm,  the  head  being  warmed  as 
well  as  the  body.  Hot  water  or  hot  coffee  is  useful.  A  little 
alcohol  or  15  drops  of  ammonia  in  one  third  of  a  glass  of 
water  every  fifteen  minutes  is  also  helpful. 

Suffocation,     In  suffocation  the  trouble  is  lack  of  oxygen, 
and  artificial  respiration  is  the  remedy. 

Bleeding.  When  a  large  artery  is  cut,  the  blood  flows  from 
it  in  spurts.  When  a  vein  is  cut,  the  blood  comes  from  it  in  a 
steady  stream.  Sometimes  the  bleeding  can  be  stopped  by 
pressing  on  the  cut  vessel  with 
the  fingers.  If  an  artery  has 
been  cut,  the  pressure  must  be 
applied  between  the  wound  and 

the  heart.      If  a  vein   has  been 

• 

cut,  the  pressure  should  be  ap- 
plied on  the  side  of  the  wound 
away  from  the  heart.  Can  you 
explain  why  this  is  the  case  ? 
When  the  wound  is  in  a  limb, 
a  handkerchief  or  other  piece 
of  cloth  should  be  knotted  and 
tightly  twisted  about  the  limb, 
as  shown  in  Figure  135.  The 
knot  in  the  handkerchief  should 
be  placed  over  the  cut  blood 
vessel,  and  if  this  does  not 


FlG.  135.     Stopping  bleeding  from 
an  artery  in  the  leg. 


stop  the  bleeding,  a  small  stone  or  a  piece  of  wood  should  be 
slipped  under  the  knot.  The  best  place  to  close  an  artery  in 
the  leg  is  on  the  inside  of  the  thigh,  or  behind  the  knee, 
because  at  these  points  the  arteries  can  be  pressed  against 
the  bones.  The  upper  arm  is  the  easiest  place  to  cut  the 
blood  off  from  the  arm.  When  the  wound  is  in  a  part  of  the 


2/8 


HUMAN  PHYSIOLOGY 


FIG.  136.    Stopping  bleeding 
from  an  artery  in  the  arm. 


body  around  which  something  cannot  be  twisted,  cloths  should 
be  folded  and  pressed  down  on  the  wound.     Any  part  of  the 

body  from  which  blood  is  escaping 
should  be  raised,  for  the  blood  al- 
ways flows  more  easily  to  a  part  of 
the  body  that  is  lowered. 

Fainting.  Fainting  is  caused  by  a 
lack  of  blood  in  the  brain.  In  treat- 
ing a  person  who  has  fainted,  it  is 
most  important  to  lay  him  flat  and 
loosen  all  clothing  about  the  neck  so 
that  the  blood  can  readily  flow  to 
the  head.  Fresh  air  is  beneficial, 
and  sprinkling  the  face  with  cold 
water  or  causing  the  patient  to  smell 
ammonia  salts  may  assist  in  bring- 
ing him  back  to  consciousness.  When  fainting  is  followed  by 
weakness,  a  few  drops  of  ammonia  in  a  little  water  (15  drops 
of  ammonia  in  one  third  of  a  glass  of  water  for  an  adult) 
will  prove  a  helpful  stimulant. 

Sunstroke.  Lay  the  patient  in  the  shade  and  pour  cold 
water  on  or  apply  ice  to  the  head,  back  of  the  neck,  and 
spine. 

Foreign  Bodies  in  the  Eye.  Foreign  particles  may  be  re- 
moved from  the  eye  by  turning  back  the  eyelid  over  a  match 
or  similar  object,  and  wiping  off  the  foreign  body.  The  eye 
should  not  be  rubbed  or  the  particle  may  become  embedded 
in  the  lining  of  the  eyelid  or  in  the  outer  surface  of  the  eye. 
Holding  up  the  eyelid  while  the  eye  is  moved  about  sometimes 
brings  the  particle  down  to  where  it  can  be  removed.  Some- 
times the  offending  body  may  be  washed  out  by  bathing 
the  eye. 


ACCIDENTS  279 

Burning  Clothing.  If  your  clothing  should  take  fire,  do 
not  start  to  run.  Lie  down  and  wrap  yourself  in  a  rug, 
blanket,  or  anything  you  can  lay  hands  on,  to  smother  the 
flames.  If  no  rug  or  blanket  is  at  hand,  lie  down  and  roll 
over  and  over.  In  any  case  be  sure  and  lie  down  to  prevent 
the  flames  from  coming  up  around  your  face,  for  inhaling  a 
flame  is  often  fatal. 

When  the  clothing  of  another  person  is  on  fire,  wrap  him 
in  something  to  smother  the  flames,  and  throw  him  down. 
Protect  your  own  face  as  much  as  possible  while  doing  this. 
In  a  burning  building  hold  something  before  your  face  when 
near  a  flame. 

Treatment  of  Burns.  Moisten  the  clothing  with  water  and 
clip  it  away  from  the  wound.  Do  not  tear  the  skin.  Rather 
than  do  this,  leave  patches  of  clothing  sticking  to  the  wound. 
Blisters  should  not  be  broken,  but  the  liquid  in  them  should 
be  drained  off  by  making  small  holes  with  a  needle  in  the 
sides  of  the  blisters.  The  treatment  for  burns  made  with  hot 
water  is  the  same. 

Shut  tJie  air  off  from  the  burn.  The  following  are  conven- 
ient methods  of  doing  this  : 

Cover  the  wound  with  clean  cotton  cloths  that  have  been 
dipped  in  olive  (sweet)  oil.  If  carbolic  acid  and  glycerin  are 
at  hand,  add  a  teaspoonful  of  each  to  a  pint  of  the  oil  before 
it  is  used. 

Stir  baking  soda  into  vaseline  and  cover  the  wounds  with 
cloths  on  which  this  has  been  spread. 

Soak  cloths  in  water  in  which  as  much  soda  as  possible 
has  been  dissolved,  and  spread  them  over  the  wound. 

When  nothing  else  is  at  hand,  cover  the  wound  with  white 
of  egg,  wet  starch,  or  wet  flour.  Do  not  cover  a  burn  with 
cotton,  or  the  cotton  will  stick  to  the  flesh  and  cause  trouble. 


280  HUMAN  PHYSIOLOGY 

Great  care  should  be  used  to  keep  a  burn  from  becoming 
infected  with  germs  (page  312).  Unless  it  does  become  in- 
fected, it  is  best  not  to  open  it  for  some  time,  but  to  keep  the 
cloths  with  which  it  is  covered  moist  with  sweet  oil  in  which 
there  is  a  little  carbolic  acid  and  glycerin. 

Poisoning.  When  any  poison  except  an  acid  has  been 
swallowed,  vomiting  should  be  induced  at  once.  To  cause 
the  vomiting,  stir  a  tablespoonful  of  mustard  in  a  glass  of 
water,  take  half  of  it,  drink  a  large  quantity  of  hot  water, 
and  follow  it  with  the  remainder  of  the  mustard.  Large 
amounts  of  warm  salt  water  or  simply  warm  water  may  be 
used  when  no  mustard  is  at  hand.  Tickling  the  throat  with 
a  feather  or  thrusting  the  finger  down  the  throat  will  often 
bring  on  the  vomiting. 

Acids.  Give  soda,  chalk,  old  mortar,  or  soap  in  plenty  of 
warm  water,  and  then  cause  vomiting.  Oil  and  milk  are  also 
useful.  For  carbolic  acid,  oil  or  milk  is  best. 

Arsenic.  Cause  vomiting  and  give  hydrated  sesquioxid  of 
iron.  This  compound  may  be  formed  by  adding  tincture  of 
iron  to  baking  powder.  Give  some  of  the  brown  powder 
that  is  formed  to  the  patient  every  few  minutes.  The  poison 
in  Paris  green,  Fowler's  solution,  and  Rough  on  Rats  is 
arsenic,  and  the  treatment  for  poisoning  with  them  is  the 
same  as  the  treatment  for  poisoning  with  arsenic. 

Belladonna.  This  is  the  poison  in  nightshade.  Use  the 
treatment  for  it  that  is  given  below  for  opium. 

Mercuric  Chlorid.  (Also  called  bichlorid  of  mercury  and 
corrosive  sublimate.)  Give  milk  and  white  of  egg  or  both. 
Flour  or  starch  with  milk  and  eggs  is  also  a  good  remedy. 

Phosphorus.  Magnesia  and  chalk  in  water  and  the  white 
of  egg  are  good  remedies.  Do  not  give  oil  or  milk.  Phos- 
phorus is  in  the  substance  on  the  ends  of  matches,  and  phos- 


ACCIDENTS  28l 

phorus  poisoning  usually  comes  from    allowing    children  to 
play  with  matches. 

Opium.  Give  strong  coffee  or  ammonia  (15  drops  in  one 
third  of  a  glass  of  water  every  fifteen  minutes  or  oftener). 
Walk  the  patient  about,  slap  him,  throw  cold  water  on  him, 
and  do  not  allow  him  to  go  to  sleep.  Morphine,  laudanum, 
cholera  mixtures,  paregoric,  and  soothing  syrups  are  all  either 
forms  of  opium  or  contain  it. 

Strychnin.  Inhaling  chloroform  or  ether  will  quiet  the 
patient.  Give  five  grains  of  sodium  bromid  every  half  hour. 
Ammonia  (see  under  Opium)  or  camphor  in  water  is  useful. 
Throw  cold  water  over  the  patient  and  use  artificial  respira- 
tion if  necessary. 

Stramonium.  This  is  the  poisonous  substance  in  Jimson 
weed.  The  treatment  for  poisoning  with  it  is  the  same  as 
the  treatment  for  opium  poisoning. 

It  is  to  be  remembered  that  in  poisoning  with  any  of  the 
above  substances  except  acids,  one  of  the  most  important 
things  is  to  cause  vomiting  promptly.  In  acid  poisoning  it 
is  usually  best  to  give  something  to  destroy  the  acid  (page 
280)  before  the  vomiting  is  induced. 

Summary.  In  accidents  and  emergencies  a  cool  head  and 
prompt  action  are  important. 

It  is  much  easier  for  a  person  to  keep  afloat  when  his 
body  is  low  in  the  water  than  when  he  tries  to  climb  up 
out  of  the  water.  To  revive  a  person  who  has  been  under 
water,  the  water  should  be  drained  from  the  lungs  and  artificial 
respiration  started  at  once.  This  should  be  kept  up  for  at 
least  two  hours.  It  is  also  important  to  keep  the  patient 
warm. 

Suffocation  is  due  to  lack  of  oxygen,  and  artificial  respira- 
tion is  the  treatment  for  it. 


282  HUMAN  PHYSIOLOGY 

Bleeding  from  a  large  vessel  may  be  stopped  by  pressing 
on  and  closing  the  vessel.  Fainting  persons  should  be  laid 
flat  so  that  the  blood  will  flow  to  the  head.  In  sunstroke 
the  patient's  head  and  spine  should  be  cooled. 

Running  when  the  clothes  are  on  fire  fans  the  flames.  In 
such  an  emergency  one  should  lie  down  and  smother  the 
flames  with  a  rug  or  blanket,  or  put  them  out  by  rolling  over 
and  over.  In  all  cases  of  fire,  care  should  be  taken  not  to 
inhale  the  flame.  In  a  burn  the  skin  should  not  be  torn,  but 
the  wound  should  be  covered  from  the  air. 

In  poisoning,  vomiting  to  get  the  poison  out  of  the  stomach 
is  a  very  important  part  of  the  treatment.  In  acid  poison- 
ing it  is  best  to  give  something  to  destroy  the  acids  before 
vomiting  is  caused.  Other  treatment  should  be  given  accord- 
ing to  the  poison. 

QUESTIONS 

In  trying  to  keep  afloat,  where  should  the  body  be  allowed  to 
remain?  What  causes  death  in  drowning?  In  attempting  to  re- 
vive an  apparently  drowned  person,  what  is  the  important  thing  to 
do? 

What  is  the  first  thing  to  do  in  attempting  to  revive  a  person  who 
has  been  under  water?  How  is  this  done ?  In  what  position  should 
the  patient  then  be  laid?  Why  must  care  be  exercised  in  regard  to 
the  tongue?  Explain  how  artificial  respiration  may  be  carried  on 
by  one  person  ;  by  two  persons.  How  long  should  it  be  continued  if 
the  patient  does  not  sooner  revive?  Describe  another  method  that 
one  person  may  use  in  causing  artificial  respiration.  What  is  the 
advantage  of  this  method?  What  other  treatment  should  be  given 
where  possible? 

What  causes  death  in  suffocation?  What  treatment  should  be 
given? 


ACCIDENTS  283 

When  a  large  artery  is  cut,  how  does  the  blood  flow  from  it? 
How  does  the  blood  flow  from  a  vein  ?  Where  should  pressure  be 
applied  to  close  a  cut  artery?  a  vein?  Explain  how  bleeding  from 
a  cut  in  a  limb  may  be  stopped.  Where  is  the  best  place  to  apply 
pressure  to  shut  off  the  blood  from  the  leg  ?  from  the  arm  ?  How 
may  bleeding  from  a  cut  in  some  other  part  of  the  body  be  stopped? 

What  causes  fainting  ?  How  should  a  fainting  person  be  treated  ? 
What  treatment  should  be  given  in  sunstroke  ? 

What  should  one  not  do  if  his  clothing  takes  fire  ?  What  are  the 
best  ways  of  extinguishing  the  flame  ?  Why  is  it  important  to  pro- 
tect the  face  from  flame? 

What  two  important  points  should  be  kept  in  mind  in  dressing  a 
burn  ?  How  may  the  air  be  kept  from  a  burn  ? 

What  is  an  important  part  of  the  treatment  in  poisoning? 


284  HUMAN  PHYSIOLOGV 


REVIEW   QUESTIONS 

CHAPTER  XVI.  How  does  the  nervous  system  resemble  a  telephone 
system  ?  Give  the  functions  of  the  cerebrum ;  of  the  cerebellum ; 
of  the  pons ;  of  the  medulla ;  of  the  spinal  cord.  Explain  how  a 
reflex  action  is  carried  out.  Define  :  ganglion  ;  neuron  ;  afferent ; 
efferent ;  convolutions  ;  arbor  vitae  ;  acquired  reflex. 

CHAPTER  XVII.  How  many  pairs  of  cranial  nerves  are  there?  of 
spinal  nerves  ?  Which  roots  of  the  spinal  nerves  contain  the  afferent 
and  which  the  efferent  fibers?  (This  may  be  fixed  in  the  mind  by 
remembering  that  the  first  letters  of  the  words  dorsal  and  afferent, 
and  of  ventral  and  efferent,  spell  Dave.}  What  is  the  function  of  the 
sympathetic  system?  Explain  how  a  sympathetic  reflex  is  carried 
out.  How  much  sleep  is  needed  by  a  person  of  your  age?  What 
are  the  effects  of  tobacco  on  the  nervous  system?  of  alcohol? 

CHAPTER  XVIII.  How  is  alcohol  formed?  What  is  its  effect  on 
length  of  life?  on  the  death  rate  from  tuberculosis?  What  per  cent 
of  insanity  is  caused  by  alcohol?  Give  some  facts  that  show  that  the 
evil  effects  of  alcohol  are  inherited.  Speak  of  the  effects  of  alcohol 
on  the  character. 

CHAPTER  XIX.  Name  the  special  senses.  How  is  the  sensation 
of  feeling  caused?  of  taste?  of  smell?  How  may  the  olfactory  cells 
be  injured  ?  How  does  a  wave  in  the  air  cause  a  sensation  of  sound? 
Mention  some  ways  in  which  the  ears  may  be  injured.  Define  : 
auditory  canal ;  tympanic  membrane;  tympanum;  malleus;  incus; 
stapes  ;  Eustachian  tube  ;  vestibule ;  cochlea. 

CHAPTER  XX.  How  is  the  eye  protected?  Draw  a  diagram  of  a 
longitudinal  section  through  the  eye.  Explain  how  an  image  is 
formed  on  the  retina.  Explain  how  the  eye  is  accommodated. 
What  is  the  trouble  in  a  near-sighted  eve?  in  a  far-sighted  eye?  in 
an  astigmatic  eye?  In  each  case  what  kind  of  spectacles  is  needed  ? 
Mention  some  points  connected  with  the  hygiene  of  the  eye. 

Define  :  lachrymal  gland  ;  retina  ;  vitreous  humor  ;  aqueous  humor  ; 
cornea ;  iris  ;  pupil ;  suspensory  ligament ;  ciliary  muscles. 

CHAPTER  XXL  Tell  how  to  revive  a  person  who  has  been  under 
water.  What  should  be  done  in  cases  of  suffocation?  of  bleeding? 
of  fainting?  of  sunstroke?  when  the  clothing  is  on  fire?  in  treating  a 
burn?  incases  of  poisoning? 


CHAPTER    XXII 

DISEASE  GERMS 

DISEASE  germs  cause  the  death  of  over  50  per  cent  of  the 
human  race.  In  addition  to  this  great  loss  of  life,  they  are 
responsible  for  an  amount  of  suffering  so  great  that  it  can 
hardly  be  imagined.  Every  year  millions  of  dollars'  worth  of 
time  is  lost  by  persons  suffering  from  diseases  caused  by 
germs;  great  amounts  of  time  and  money  are  constantly 
being  spent  in  caring  for  these  sufferers ;  and  every  year 
hundreds  of  thousands  of  people  rise  from  beds  of  sickness, 
weakened  for  life  by  diseases  caused  by  these  small  enemies 
of  mankind. 

A  great  part  of  this  suffering  and  loss  of  money,  time,  and 
life  is  unnecessary,  for  germ  diseases  are,  in  the  main,  pre- 
ventable.1 The  most  useful  facts  of  all  science,  therefore, 
are  the  facts  that  give  us  a  knowledge  of  disease  germs  and 
how  to  avoid  them. 

What  are  Disease  Germs?  One-celled  animals  are  called 
protozoa  (singular,  protozoan),  and  one-celled  plants  of  a  cer- 
tain kind  are  called  bacteria  (singular,  bacterium).  The  prin- 
cipal breeding  places  of  protozoa  and  bacteria  are  in  water 
and  in  the  earth.  To  most  kinds  of  them  we  pay  no  attention, 
for  they  are  harmless.  A  few  kinds,  however,  grow  in  the 
bodies  of  man  and  other  animals,  and  cause  sickness.  When 

1  "It  is  within  the  power  of  man  to  cause  all  parasitic  diseases  to  disappear 
from  the  world."  —  PASTEUR. 

285 


286  HUMAN  PHYSIOLOGY 

we  speak  of  disease  germs,  we  are  referring  to  the  little  ani- 
mals and  plants  that  grow  in  the  bodies  of  men  and  animals 
and  cause  disease. 

The  Multiplication  of  Disease  Germs.  All  that  most  disease 
germs  do  when  'they  multiply  is  to  grow  longer  and  pinch  in 
two.  Then  there  are  two  germs.  A  cholera  germ  may  be- 
come full-grown  and  divide  in  twenty  minutes,  and  all  disease 
germs  multiply  with  astonishing  rapidity.  If  one  germ  and 
the  germs  that  come  from  it  should  divide  at  the  rate  of  once 
an  hour,  in  twenty -four  hours  they  would  increase  to  more 
than  seventeen  millions. 

Where  Disease  Germs  come  from.  The  germ  of  typhoid 
fever  may  be  in  water,  the  smallpox  germ  on  clothes,  the 
diphtheria  germ  on  a  pencil  or  a  drinking  cup,  and  the  germ 
that  causes  consumption  may  be  in  the  dust  that  blows  about 
the  streets.  These  germs,  however,  do  not  originate  in  the 
water,  on  the  clothes  or  pencil,  or  in  the  dust,  but  in  nearly 
all  cases  they  come  from  some  human  body  in  which  they  are 
growing.  In  the  prevention  of  germ  diseases,  nothing  is  so 
important,  therefore,  as  to  keep  germs  from  the  bodies  of 
persons  who  have  these  diseases  from  being  scattered  about.1 
The  following  experiments  will  show  that  disease  may  be 
spread  by  allowing  the  little  plants  and  animals  that  cause 
them  to  get  into  new  locations  where  they  can  grow : 

1  It  is  important  to  realize  that  germs  are  plants  and  animals,  and  that  a  germ 
can  grow  only  from  another  living  germ  of  the  same  kind.  It  is  unsafe  to  have 
dirt  and  unclean  matter  about,  for  if  germs  get  into  it  they  may  live  in  it  for  a 
long  time  and  often  may  multiply  in  it;  but  the  idea  that  germs  originate  in 
such  matter  is  not  correct.  As  we  shall  see  later,  a  few  germ  diseases  may  occa- 
sionally be  contracted  from  animals,  and  people  who  are  not  themselves  sick 
may  sometimes  carry  certain  kinds  of  disease  germs  in  their  bodies.  In  most 
cases  of  germ  diseases,  however,  the  germ  comes  from  another  person  who  is 
suffering  with  the  disease. 


DISEASE  GERMS  287 

Thrust  a  needle  into  a  rotten  apple  and  then  into  a  sound  apple.1 
Lay  the  sound  apple  away  for  a  few  days  and  wait  for  the  appearance 
of  the  disease  in  it.  Cut  it  open  and  note  how  the  rot  has  spread 
out  from  the  needle  path.  The  disease  will  probably  develop  more 
quickly  if  you  will  bore  a  small,  deep  hole  in  the  side  of  the  apple 
and  pack  some  of  the  rotten  material  from  the  apple  into  it. 

Inquire  among  greenhouse  owners  and  find  a  carnation  that  is 
suffering  from  stem  rot.  Cut  into  the  diseased  stem,  and  then  with 
the  same  knife  cut  a  healthy  stem  half  in  two.  Tie  a  cloth  about  the 
wounded  stem,  and  keep  it  moist  until  the  disease  develops.  The 
disease  may  be  more  surely  produced  by  putting  into  the  wound  a 
little  matter  from  the  diseased  stem. 

How  Disease  Germs  enter  the  Body.  Sometimes  disease 
germs  enter  the  body  through  the  skin,  working  down 
through  the  hair  follicles  and  sweat  glands,  or  getting  into 
wounds.  The  germs  of  a  number  of  diseases  are  introduced 
into  the  body  by  the  bites  of  insects.  More  commonly,  germs 
enter  the  mouth  or  nose  and  grow  in  the  walls  of  the  air 
passages,  the  walls  of  the  alimentary  canal,  or  in  the  lungs. 
A  knowledge  of  how  a  germ  enters  the  body  often  helps  us 
to  avoid  the  disease  that  it  causes. 

How  Germs  cause  Sickness.  When  disease  germs  grow  in 
the  body,  they  produce  substances  called  toxins.  The  toxins 
are  very  violent  poisons,  and  cause  illness  by  poisoning  the 
cells  of  the  body.  You  should  get  clearly  in  mind  the  fact 
that  //  is  not  the  germs  themselves,  but  tJie  toxins  that  the 
germs  produce,  that  cause  the  disease.  Almost  all  fevers  are 
caused  by  the  toxins  of  disease  germs.2 

1  Rots  are  caused  by  fungi  (Fig.  151)  that  are  much  larger  than  the  bacteria 
and  protozoa  that  cause  diseases  in  our  bodies.     The  fungi  are  living   plants, 
however,  and  closely  related  to  the  bacteria;  and  rots  are  spread  by  the  spreading 
of  the  fungi  that  cause  them,  just  as  our  diseases  are  spread  by  the  spreading  of 
the  bacteria  and  protozoa  that  cause  them. 

2  Within  the  body,  substances  called  antitoxins  are  produced  to  destroy  the 
toxins.     These  are  discussed  on  page  307. 


288 


HUMAN  PHYSIOLOGY 


How  the  Body  kills  Germs.  Germs  that  get  into  the  body 
are  killed  in  two  ways  —  by  the  white  corpuscles  of  the  blood 
and  by  a  germicidal  {germ-killing}  substance  that  is  in  the 
blood.  The  white  corpuscles  flow  around  the  germs  and 
take  them  in,  or  swallow  them.  Then  the  corpuscles 
attempt  to  digest  and  kill  the  germs,  and  the  germs  try  to 
grow  in  the  corpuscles  and  use  them  for  food.  If  the  cor- 
puscles triumph,  the  germs  will  be  killed  and  the  disease 


FlG.  137.     A  white  corpuscle  taking  in  disease  germs,    a  is  a  germ  that  has  been  killed 
and  partially  broken  up  by  the  corpuscle. 

will  be  checked.  If  the  germs  are  victorious,  the  corpuscles 
will  be  destroyed,  the  disease  will  go  on,  and  the  patient  will 
finally  die. 

Just  what  the  germicidal  substance  of  the  blood  is  or  where 
it  comes  from  is  not  certainly  known,  but  there  is  something 
dissolved  in  the  blood  that  kills  germs  that  get  into  the  body. 
The  blood  of  a  healthy  person  always  has  some  germicidal 
substance  in  it  and  some  power  of  killing  germs.  When 
disease  germs  get  into  the  body,  more  of  this  substance  is 
manufactured  and  thrown  off  into  the  blood,  where  it  power- 
fully aids  the  white  corpuscles  in  the  fight  against  the  germs. 
The  turn  of  the  fever  in  germ  diseases  comes  when  the 
corpuscles  and  the  germicidal  substance  begin  to  get  the 
better  of  the  germs. 

Different  Germicidal  Substances.  There  is  a  different  ger- 
micidal substance  for  each  different  kind  of  disease  germ,  and 


DISEASE   GERMS  289 

after  recovery  from  an  attack  of  a  disease,  a  large  amount 
of  the  germicidal  substance  for  the  germ  of  that  disease  will 
be  found  in  the  blood.  The  germicidal  substance  for  some 
germs  remains  in  the  blood  for  years,  and  there  are  many 
diseases  that  people  usually  have  but  once.  This  is  because 
after  an  attack  of  one  of  these  diseases  the  germicidal  sub- 
stance remains  in  the  blood  through  life  and  promptly 
kills  any  germs  of  that  kind  that  may  get  into  the  body. 
In  other  diseases  the  germicidal  substances  quickly  disap- 
pear from  the  blood,  and  we  may  have  them  again  and  again. 
Inherited  Diseases.  It  is  often  said  that  diseases  (e.g.  con- 
sumption, leprosy,  cancer)  are  inherited.  By  this,  it  is  not 
meant  that  the  germs  of  a  disease  are  inherited,  but  that 
little  power  of  killing  those  germs  is  inherited.  If  the 
parent  has  little  power  of  killing  a  certain  germ,  the  child 
will  also  be  likely  to  have  little  power  of  killing  it.  The 
germ  may  get  into  the  body  of  the  parent,  and,  finding  little 
resistance,  attack  him.  At  another  time  it  gets  into  the 
body  of  the  child,  and  the  germicidal  power  of  the  blood 
being  slight,  the  child  is  also  attacked.  Certain  families  are 
weak  in  their  power  of  resistance  to  certain  germs,  and 
therefore  surfer  from  the  diseases  caused  by  these  germs. 
Races  of  men  differ  in  their  power  to  kill  germs,  the  Mon- 
golians particularly  being  attacked  by  leprosy,  and  the 
negro  race  having  little  resistance  to  the  germ  that  causes 
consumption.  The  germicidal  power  of  the  body  is  inherited 
in  races  as  well  as  in  families,  but  it  is  the  lack  of  power  to 
kill  the  germ,. and  not  the  germ  itself,  that  is  inherited.  A 
member  of  a  family  that  suffers  from  a  certain  disease  should 
take  special  care  to  keep  himself  free  from  the  germs  of  that 
disease,  for  as  long  as  he  can  keep  these  germs  out  of  his 
body,  he  may  be  as  healthy  as  any  one. 


2QO  HUMAN  PHYSIOLOGY 

Keeping  up  the  Germicidal  Power  of  the  Body.  The  seeds 
of  plants  lie  in  the  earth  through  the  cold  winter,  waiting  for 
the  warmth  of  spring  to  enable  them  to  grow ;  so  disease 
germs  often  He  in  the  body,  ready,  if  a  favorable  time  comes, 
to  start  their  growth.  Germs  capable  of  producing  disease 
are  usually  in  the  body,  and  the  germs  of  most  dangerous 
diseases  often  enter  the  body  at  times  unknown  to  us.  The 
only  safe  way,  therefore,  is  always  to  keep  the  body  in 
health,  so  that  it  may  be  able  to  repel  any  attacks  that  may 
be  made  upon  it.  Overwork,  hunger,  exposure  to  cold,  wet 
feet,  insufficient  sleep,  bad  ventilation,  bad  food,  lack  of  exer- 
cise, alcohol  —  all  of  these  things  injure  the  body  and  lower 
its  germicidal  power.  It  is  a  duty  that  every  one  owes  to 
himself  to  keep  his  body  in  good  condition,  and  to  fail  to  do 
so  is  no  more  sensible  than  it  would  be  for  a  garrison  in  a 
hostile  country  to  go  to  sleep  with  the  gates  of  the  fortress 
open. 

Alcohol  and  Germ  Diseases.  We  have  already  learned  that 
the  world's  greatest  authorities  on  tuberculosis  state  that  al- 
cohol drinking  renders  the  body  more  susceptible  to  the 
germ  that  causes  that  disease  (page  240).  Physicians  have 
observed  that  a  drunken  spree  sometimes  brings  on  an  attack 
of  pneumonia,  and  it  has  long  been  the  opinion  of  medical 
men  that  alcohol  drinkers  are  more  liable  to  the  attacks  of 
germ  diseases  than  are  non-users  of  alcohol. 

More  recently  it  has  been  definitely  proved  by  experiments 
on  animals  that  alcohol  lowers  the  germicidal  power  of  the 
body,  and  it  has  been  discovered  that  alcohol  paralyzes  the 
white  corpuscles  and  renders  them  unable  to  take  up  and 
destroy  disease  germs.  Knowing  this,  it  is  easy  to  understand 
why  drinking  may  bring  on  an  attack  of  a  germ  disease. 
When  pneumonia  germs  are  already  in  the  body  waiting  for 


DISEASE   GERMS  291 

a  chance  to  attack  it,  and  the  white  corpuscles  are  paralyzed 
by  drinking  alcohol,  we  need  not  be  surprised  if  the  disease 
develops. 

Summary.  Disease  germs  cause  the  death  of  over  one  half 
of  the  human  race.  They  are  small  plants  and  animals  that 
grow  in  the  body  and  multiply  with  great  rapidity.  They 
are  spread  from  the  bodies  of  those  who  are  suffering  with 
germ  diseases,  enter  the  body  in  various  ways  and  cause  dis- 
ease by  producing  a  poisonous  toxin. 

The  body  kills  germs  by  its  white  blood  corpuscles  and  by 
a  germicidal  substance  in  the  blood.  The  germicidal  sub- 
stance is  increased  during  an  attack  of  a  disease,  and  after 
recovery  may  remain  in  the  blood,  so  that  the  person  will  be 
protected  against  that  disease  for  life.  Certain  families  and 
races  of  men  are  particularly  weak  in  their  power  to  kill  cer- 
tain germs.  It  is  of  the  greatest  importance  to  keep  up  the 
germicidal  power  of  the  body.  This  is  lowered  by  alcohol. 

QUESTIONS 

What  are  disease  germs  ?  How  do  they  multiply  ?  Where  do  the 
germs  that  cause  our  diseases  come  from  ?  How  do  they  enter  the 
body  ?  How  do  they  cause  sickness  ?  How  does  the  body  kill  them  ? 
Why  do  we  usually  have  certain  diseases  only  once?  What  is  meant 
by  an  inherited  disease  ?  Why  is  it  important  to  keep  up  the  germi- 
cidal power  of  the  body?  Mention  some  ways  in  which  the  resist- 
ance of  the  body  to  germs  may  be  lowered.  How  does  alcohol  reduce 
the  power  of  the  body  to  kill  germs  ? 


CHAPTER    XXIII 

DISEASES   CAUSED   BY  PROTOZOA 

THE  protozoa  (page  285)  are  the  smallest  of  all  animals. 
The  largest  of  them  can  barely  be  seen  with  the  naked  eye, 
and  under  the  most  powerful  microscope  the  smallest  of  them 
look  like  tiny  specks.  Some  of  those  living  in  the  ocean  have 
shells,  and  so  abundant  are  they  that  great  beds  of  chalk  and 
limestone  are  built  by  them.  Others  are  phosphorescent, 
and  in  the  warmer  seas  the  waves  at  night  are  often  fringed 
with  light  from  the  multitude  of  protozoa  in  the  water. 
They  are  abundant  in  fresh  water  also,  every  pool  and  pud- 
dle containing  great  numbers  of  them,  and  they  grow  as 
parasites  in  almost  every  animal  from  worms  and  insects  up 
to  man.  Some  of  our  worst  diseases  are  caused  by  protozoa. 

MALARIA 

Malaria  is  one  of  the  .worst  diseases  that  afflict  mankind. 
No  community  or  portion  of  a  country  can  reach  its  highest 
state  of  development  as  long  as  malaria  is  prevalent  in  it ; 
for  the  disease  affects  a  large  number 1  of  the  inhabitants, 
and  persons  so  affected  do  not  have  and  cannot  have  the 
strength,  energy,  and  ambition  necessary  to  carry  on  great 

1  In  malarial  countries  the  germ  is  sometimes  found  in  the  blood  of  from  20  to 
60  per  cent  of  the  inhabitants.  In  many  instances  the  disease  takes  a  slow 
chronic  form  in  which  the  patient  does  not  have  chills  and  fever,  and  often  does 
not  know  that  he  is  suffering  from  the  disease,  The  germ  may  remain  in  the 
body  for  years. 

292 


DISEASES   CAUSED   BY  PROTOZOA 


293 


enterprises.  Many  of  the  most  backward  portions  of  our 
country  would  in  a  very  few  years  be  centers  of  industry, 
education,  and  leadership,  if  malaria  could  be  eradicated  from 
them. 

The  Cause  of  Malaria.  Malaria  is  caused  by  protozoa  that 
live  in  the  red  corpuscles  of  the  blood.  The  protozoon  in- 
creases in  size  until  it  almost 
fills  the  corpuscle.  Then 
it  divides  into  a  number  of 
parts,  each  of  which  is  a 
young  germ.  These  break 
out  of  the  corpuscle  into 
the  blood,  and  then  each 
one  settles  upon  and  en- 
ters a  fresh  red  corpuscle. 
Within  the  corpuscle  the 
germ  grows  and  the  young 
break  forth  in  due  time  to 
repeat  the  process. 

During      their      growth 


—    s~^\JS        ^^    /  -/^        -" 


Frc.  138.     The  malaria  germ  in  a  red  blood 
corpuscle.     A,  13,  and  C  show  the  growth  of 


Within     the    Corpuscles    the       the  germ  ;  Z>  shows  it  dividing  into  a  number 
i  ,  of   young  germs ;    £    shows    the    corpuscle 

malaria      germs      produce     brokeil  down  and  the  young  germs  escaping 
toxin.      At  the  time  when     into  the  blood, 
the  young  break  down  the 

corpuscles  and  come  out  into  the  blood,  a  great  amount  of 
this  toxin  is  liberated  in  the  blood  at  once,  and  the  result  is  a 
chill  and  fever.  In  addition  to  injuring  the  body  with  its 
toxin,  the  malaria  germ  destroys  millions  of  the  red  blood 
corpuscles,  thus  interfering  with  the  oxygen-carrying  power 
of  the  blood. 

Kinds  of  Malaria  Germs.     There  are  several  different  va- 
rieties of  the  malaria  germ,  some  of  which  produce  a  more 


294  HUMAN  PHYSIOLOGY 

severe  form  of  the  disease  than  others.  In  one  form  of  the 
disease  the  germ  requires  seventy-two  hours  to  complete  its 
growth  and  break  out  of  the  corpuscles.  In  this  kind  of 
malaria,  the  chill  comes  every  third  day.  In  other  forms,  the 
germs  require  forty-eight  hours  for  their  development,  and 
in  these  kinds  of  malaria  the  chill  comes  every  other  day. 
It  is  quite  possible,  however,  to  have  more  than  one  crop  of 
the  germs  in  the  blood  at  one  time.  One  set  of  germs  may 
break  out  of  the  corpuscles  one  day  and  a  different  set  the 
next  day,  so  that  the  affected  person  may  have  a  chill  every 
day.  In  some  cases  of  malaria  the  germs  may  keep  coming 
out  all  the  time  and  the  patient  may  have  a  continuous  fever. 
Usually  a  malarial  fever  rises  and  falls,  and  for  this  reason 
a  continuous  malarial  fever  is  often  called  remittent  fever. 

How  the  Malaria  Germ  enters  the  Body.  The  malaria  germ 
is  introduced  into  the  body  by  a  certain  species  of  mosquito 
.(Fig.  152).  A  mosquito  feeds  on  man  by  inserting  its  pro- 
boscis through  the  skin  and  sucking  out  the  blood.  When  a 
mosquito  draws  blood  from  a  person  who  is  affected  with 
malaria,  it  takes  malaria  germs  into  its  stomach.  The  germs 
enter  the  wall  of  the  mosquito's  stomach,  and  multiply  there, 
and  many  of  them  finally  reach  the  mosquito's  salivary 
glands. 

The  opening  in  the  proboscis  of  a  mosquito  is  too  fine 
to  allow  red  blood  corpuscles  to  pass  through  it.  The  mos- 
quito, therefore,  when  it  thrusts  its  proboscis  through  the 
skin  to  feed,  injects  saliva  down  through  its  proboscis  into 
the  wound  to  break  up  and  digest  the  red  corpuscles.  If 
the  mosquito  is  infected  with  malaria,  the  germs  will  be 
injected  into  the  wound  with  the  saliva.  The  germs  thus 
introduced  into  the  body  enter  the  red  blood  corpuscles,  and 
about  a  week  later  the  disease  develops. 


DISEASES   CAUSED   BY  PROTOZOA  295 

Curing  Malaria.  After  the  germs  of  most  diseases  get 
into  the  body,  it  is  impossible  to  kill  them  by  taking  medi- 
cines. The  germs  are  harder  to  kill  than  our  own  cells,  and 
we  cannot  poison  them  with  medicines  without  poisoning  our 
own  bodies.  Fortunately,  the  human  body  can  endure  an 
amount  of  quinine  that  will  poison  and  kill  the  germ  of  mala- 
ria.1 Malaria  is,  therefore,  one  of  the  few  germ  diseases  that 
can  be  successfully  treated  by  taking  medicine  to  kill  the 
germ.  It  is  far  better,  however,  to  prevent  the  disease  than 
to  try  to  cure  it. 

The  Prevention  of  Malaria.  Man  gets  the  malaria  germ 
from  the  mosquito,  and  the  mosquito  gets  it  from  man.  If  we 
could  destroy  all  mosquitoes,  the  disease,  of  course,  would  die 
out.  If  we  could  destroy  all  the  germs  that  are  in  the  blood 
of  malaria  patients,  the  mosquitoes  would  not  become  infected, 
and  the  disease  would  cease  to  be  spread.  The  following 
suggestions  for  the  prevention  of  malaria  are  in  accordance 
with  these  principles,  and  by  following  them  out  much  can  be 
done  to  check  the  disease : 

Screening  Malaria  Patients.  It  is  very  important  to  keep 
a  malarial  patient  under  mosquito  netting  until  the  germs  dis- 
appear from  his  blood.  Where  this  is  not  done,  it  has  been 
found  that  the  mosquitoes  in  the  house  become  infected  by 
biting  him,  and  that  other  persons  in  the  house  usually 
contract  the  disease.  In  regions  where  there  is  only  an 
occasional  case  of  malaria,  or  where  only  a  few  persons  are 
living  close  together  (as  in  a  country  farmhouse),  this  pre- 
caution will  do  much  to  prevent  the  spread  of  malaria. 

Avoiding  Unnecessary   Exposure   to  Mosquitoes.     Persons 

1  Malaria  germs  are  killed  much  more  easily  by  quinine  while  they  are  free  in 
the  blood  than  when  in  the  corpuscles.  The  q-iinine  should  be  taken  so  that  it 
will  be  in  the  blood  at  the  time  when  the  germs  come  out  of  the  corpuscles. 


296  HUMAN  PHYSIOLOGY 

living  in  malarial  regions  should  keep  their  houses  carefully 
screened  and  should  sleep  under  mosquito  nets  during  the 
mosquito  season.  They  should  not  expose  themselves  to  the 
attacks  of  mosquitoes  very  early  in  the  morning  or  late  in  the 
day,  and  should  take  care  to  avoid  the  haunts  of  the  mosqui- 
toes on  cloudy  days  when  mosquitoes  are  flying.  Judgment 
should  be  exercised  in  selecting  places  to  be  visited  in  camping 
and  fishing  excursions,  for  one  night  spent  among  mosquitoes 
may  start  an  attack  of  malaria  that  will  last  for  months. 

The.  Use  of  Quinine.     Quinine  frees  the  blood  from  malaria 
germs,  and  thus  prevents  mosquitoes  from  becoming  infected. 
A   little   quinine   in   the   blood   will   also    kill   any    malaria 
germs  that  may  be  introduced  into  the  body  by  an  infected 
mosquito,  and  thus  prevent  the  development  of 
the  disease.     In  malarial  regions  it  is  sometimes 
advisable    to   take   small  doses    of  quinine  daily 
as  a  preventive  measure. 

Destroying  Mosquitoes.  This  is  the  most 
effective  of  all  the  measures  that  are  employed 
in  fighting  malaria.  The  subject  will  be  dis- 
cussed in  a  later  chapter  (page  323). 

FIG.  139.  DYSENTERY 

The  amoeba 

of  dysentery.  Chronic  dysentery  is  usually  caused  by  a  pro- 
The  three  dark  tozoon,  an  amoeba,  that  is  similar  in  many  ways 

Ihf65  amctba  to  a  large  white  blood  corpuscle.  The  disease 
are  red  blood  is  most  common  in  the  tropics,  but  is  found  in 
corpuscles  on  Qur  own  coun^ry.  The  amoeba  of  dysentery  lives 

which     it    has  J  J 

been  feeding,     in  water,  and  when  swallowed,  enters  the  wall 
of    the  large  intestine    and    grows    there.     The 
disease  comes  from  impure  water,  and  the  best  methods  of 
preventing  it  will  be  taken  up  in  another  chapter. 


DISEASES   CAUSED   BY  PROTOZOA 


SMALLPOX 


297 


Smallpox  is  probably  caused  by  a  small  protozob'n  that 
lives  in  the  cells  of  the  skin  and  of  certain  other  parts  of  the 
body.1  The  germs  may  be  carried  on 
clothing  or  anything  that  a  smallpox  pa- 
tient touches,  and  there  are  great  numbers 
of  germs  in  the  dried  scales  that  come  from 
the  skin  during  recovery  from  the  disease. 
As  smallpox  germs  may  remain  alive  for  FIG 
months  after  being  dried  and  scattered,  smallpox  in  the  ceils  of 
the  disease  is  very  easily  spread.  For  this  the  skin- 
reason  a  person  suffering  from  smallpox  should  be  quaran- 
tined, and  everything  that  has  been  about  him  should  be 
burned  or  disinfected  (page  332).  The  incubation  period  of 
smallpox  (the  time  between  the  entrance  of  the  germs  into 
the  body  and  the  appearance  of  the  disease)  is  usually  from 
ten  to  twelve  days. 

Vaccination.  Before  vaccination  was  discovered,  smallpox 
was  one  of  the  hardest  of  all  diseases  to  control.  Up  to  a 
little  over  one  hundred  years  ago,  about  95  per  cent  of  all 
persons  were  attacked  by  it,  and  the  number  of  deaths  from 
smallpox  was  enormous.  About  the  year  1800  vaccination 
began  to  be  practiced,  and  in  all  civilized  countries  it  is  now 
more  or  less  compulsory.  Where  vaccination  is  thoroughly 
carried  out,  smallpox  has  almost  ceased  to  exist,  but  in  coun- 
tries where  the  people  are  not  vaccinated,  or  where  only  part 

1  There  is  still  some  uncertainty  in  regard  to  the  germ  of  smallpox,  some  of 
those  who  have  studied  the  bodies  shown  in  Figure  140  holding  that  they  are  not 
the  germs  that  cause  the  disease.  It  is  certain,  however,  that  smallpox  is  a 
germ  disease,  and  we  have  learned  how  to  control  it  even  if-  we  are  not  certain 
as  to  the  exact  germ  that  causes  it. 


298  HUMAN  PHYSIOLOGY 

of  them  are  vaccinated,  it  is  still  impossible  to  prevent  the 
spread  of  the'  disease.1 

How  Vaccination  protects  against  Smallpox.  The  germ  of 
smallpox  flourishes  in  man.  It  grows  in  cattle  also,  causing 
the  disease  called  cowpox.  After  growing  in  the  cow  this 
germ  seems  to  be  weakened  and  changed  so  that  it  grows 
feebly  in  man  and  has  only  a  slight  power  of  producing 
disease. 

In  vaccination,  germs  from  a  cow  are  put  into  the  human 
body.  Here  they  grow  and  begin  to  produce  the  mild  inflam- 
mation that  follows  vaccination.  The  body  now  works  up  the 
germicidal  substance  for  these  germs  and  kills  them  out 
before  they  can  make  much  growth  and  spread  through  the 
body.  After  this  is  done,  the  germicidal  substance  remains 
in  the  blood,  and  if  any  smallpox  germs  get  into  the  body,  the 
germicidal  substance  is  there  to  kill  them. 

From  this  you  will  understand  that  a  person  who  has  been 
successfully  vaccinated  is  in  very  much  the  same  condition 
as  a  person  who  has  had  a  light  attack  of  smallpox.  After 

1  In  1874  Germany  passed  a  compulsory  vaccination  law  requiring  that  every 
child  be  vaccinated  within  a  year  after  birth,  and  that  every  pupil  in  an  educa- 
tional institution  be  vaccinated  between  the  ages  of  thirteen  and  fourteen  years. 
Under  this  law,  from  1893  to  ^98  Germany  had  287  deaths  from  smallpox. 
During  this  time  there  were  many  epidemics  of  smallpox  in  other  European 
countries  where  only  part  of  the  people  had  been  vaccinated.  In  the  same  five 
years  Russia  had  over  275,000  deaths  from  the  disease,  Spain  nearly  24,000, 
Hungary  over  12,000,  and  Italy  and  Austria  each  over  11,000.  Before  the 
American  occupation  of  the  Philippine  Islands,  only  a  part  of  the  inhabitants  of 
the  Islands  had  been  vaccinated,  and  thousands  of  deaths  from  smallpox  occurred 
every  year.  The  people  have  now  been  thoroughly  vaccinated,  and  in  1907  there 
was  not  a  single  death  from  the  disease  in  the  Islands.  There  is  no  doubt  that 
the  decrease  in  the  death  rate  is  due  to  vaccination,  for  quarantining  has  failed 
to  prevent  a  considerable  amount  of  certain  other  diseases  (diphtheria,  scarlet 
fever,  etc.)  that  are  much  less  contagious  than  smallpox. 


DISEASES   CAUSED  BY  PROTOZOA  299 

vaccination,  as  after  recovery  from  an  attack  of  many  germ 
diseases,  the  germicidal  substance  in  the  blood  becomes 
weaker  and  weaker,  but  never  entirely  disappears.  Just  when 
it  becomes  so  weak  that  revaccination  is  necessary,  it  is  im- 
possible to  say.  A  successful  vaccination  usually  protects 
from  smallpox  for  several  years.  Sometimes  the  germicidal 
substance  in  the  blood  is  fairly  strong  after  seven,  eight, 
nine,  or  ten  years.  Two  successful  vaccinations  usually 
protect  against  smallpox  for  life,  but  in  a  very  few  persons 
the  germicidal  substance  disappears  so  rapidly  after  vaccina- 
tion that  the  disease  may  be  contracted  in  nine  months.  The 
safest  way  is  to  be  vaccinated  every  few  years,  and  when 
smallpox  is  prevalent,  to  be  revaccinated  if  more  than  nine 
months  have  passed  since  the  last  vaccination.  There  can 
be  no  mistake  in  this,  for  if  the  germicidal  substance  is  still 
strong  in  the  blood,  all  the  germs  put  in  by  vaccination  will 
be  killed,  and  the  vaccination  will  not  take.  If  the  vaccina- 
tion does  take,  it  is  a  sure  sign  that  the  germicidal  power  of 
the  body  had  run  low  and  that  revaccination  was  needed. 

RABIES   (HYDROPHOBIA) 

Rabies  is  believed  to  be  caused  by  a  protozoon  that  grows 
in  the  nerve  tissue.  This  germ  attacks  not  only  man,  but 
also  many  of  the  lower  animals.  It  is  found  in  the  saliva  of 
animals  suffering  from  the  disease,-  and  usually  gets  into  the 
human  system  through  the  bites  of  rabid  animals.  Practically 
all  the  rabies  in  our  country  comes  from  the  bites  of  dogs, 
and  it  would  be  possible  by  properly  muzzling  dogs  to  stamp 
out  the  disease  entirely,  as  has  been  done  in  several  Eu- 
ropean countries.  It  is  a  mistake  to  think  that  rabies  de- 
velops in  dogs  because  of  hot  weather,  for  they  get  the 


300  HUMAN  PHYSIOLOGY 

germ  from  the  bites  of  other  dogs  and  may  have  the  disease 
at  any  time  of  the  year. 

In  man  the  germ  of  rabies  grows  very  slowly.  At  least 
two  weeks  are  required  after  the  germs  are  introduced 
into  the  body  before  the  disease  shows  itself.  Usually  the 
disease  does  not  develop  for  five  or  six  weeks,  and  some- 
times not  for  a  year.  There  is  no  cure  for  rabies  after  the 
disease  develops,  but  a  preventive  treatment,  founded  on  the 
same  principles  as  vaccination,  was  discovered  by  a  great 
French  scientist  named  Louis  Pasteur.  The  Pasteur  treat- 
ment is  successful  in  nearly  all  cases  in  which  it  is  com- 
menced in  time.  Where  the  materials  for  this  treatment  can 
be  delivered  within  thirty-six  hours,  they  can  be  sent  by  mail 
and-  the  treatment  given  to  the  patient  by  his  home  physician. 
No  time  should  be  lost  in  beginning  the  treatment. 

The  Treatment  of  Wounds  made  by  Rabid  Animals.  A 
very  great  safeguard  against  this  disease  is  to  treat  promptly 
wounds  made  by  the  teeth  of  animals  with  something  that 
will  kill  the  germs  in  the  wounds.  Any  disinfectant  (page 
334)  is  useful,  but  burning  with  nitric  acid  is  the  most  effec- 
tive remedy.  This  should  be  done  by  a  physician  to  make 
sure  that  it  is  thoroughly  done,  and  to  guard  against  too  great 
injury  to  the  flesh  by  the  acid.  The  best  method  is  to  apply 
at  once  to  the  wound  any  disinfectant  that  may  be  at  hand 
and  then  have  it  treated  as  soon  as  possible  by  a  physician. 
Treatment  of  the  wound  even  after  twenty-four  hours  is 
useful.  An  animal  that  has  bitten  any  one  should  not  be 
killed,  but  should  be  confined  until  it  is  known  whether  or 
not  it  has  hydrophobia.  If  the  animal  remains  in  health  for 
nine  or  ten  days,  there  will  then  be  no  occasion  for  worry. 

Other  Protozoan  Diseases.  In  the  tropics  many  diseases  of 
man  are  caused  by  protozoa.  Among  these  diseases  are  the 


DISEASES   CAUSED   BY  PROTOZOA  301 

slow  and  fatal  sleeping  sickness  of  Africa,  which  is  commu- 
nicated to  man  by  a  fly.  It  is  thought  that  scarlet  fever, 
measles,  and  possibly  cancer,  are  caused  by  protozoa,  but 
these  diseases  are  not  thoroughly  understood.  Rocky  Moun- 
tain or  "spotted"  fever,  a  disease  of  the  Rocky  Mountains, 
which  is  caused  by  the  bite  of  a  tick,  is  almost  surely  a 
protozoan  disease.  A  protozoon  that  is  carried  by  a  tick 
causes  the  "  Texas  fever  "  or  "tick  fever"  that  is  prevalent 
among  cattle  in  our  Southern  states,  and  in  the  tropics  many 
fatal  diseases  of  animals  are  caused  by  protozoa. 

Summary.  Protozoa  cause  many  diseases  of  man. 
Among  them  are  malaria,  dysentery,  smallpox,  and  rabies. 
The  germs  of  malaria  are  carried  by  the  mosquito,  and  the 
disease  may  be  escaped  by  avoiding  mosquitoes.  Dysen- 
tery usually  comes  from  impure  .water.  The  germ  of 
smallpox  is  easily  spread,  and  few  persons  naturally  have 
the  power  to  resist  it.  By  vaccination  the  germicidal 
power  of  the  body  toward  the  smallpox  germ  may  be 
raised  and  the  disease  controlled.  Rabies  comes  from  the 
bites  of  dogs.  Generally  the  disease  can  be  prevented 
from  developing  by  the  Pasteur  treatment.  Wounds  made 
by  the  teeth  of  animals  should  be  disinfected.  Protozoa 
cause  other  diseases  of  animals  and  men. 


QUESTIONS 

Why  is  malaria  an  important  disease?  Describe  the  life  history 
of  the  malaria  germ.  What  causes  the  chill  in  malaria?  How 
does  the  malaria  germ  enter  the  body?  How  long  is  it  after  the 
germ  gets  into  the  body  before  the  disease  appears?  How  may  the 
malaria  germ  be  killed  in  the  blood?  How  may  malaria  be  pre- 
vented? Where  does  the  germ  of  dysentery  grow  in  the  body?  How 


302  HUMAN  PHYSIOLOGY 

does  it  get  into  the  body?  How  may  smallpox  germs  be  spread? 
What  is  the  incubation  period  of  the  disease  ?  What  per  cent  of 
people  had  smallpox  before  vaccination  was  practiced?  Explain 
how  vaccination  protects  the  body.  How  often  should  one  be 
vaccinated  ? 

How  does  the  germ  of  rabies  enter  the  body  ?  How  may  the 
disease  be  stamped  out?  What  is  the  incubation  period  of 
rabies?  How  may  the  development  of  the  disease  be  prevented? 
How  should  wounds  made  by  the  teeth  of  animals  be  treated? 
Name  some  other  diseases  that  are  thought  to  be  caused  by  pro- 
tozoa. 


In  some  parts  of  our  country  there  is  no  malaria.  Why  is  this  the 
case  ?  Sometimes  persons  who  have  been  living  in  a  malarial  region 
have  chills  and  fever  when  they  move  into  a  region  where  there  is  no 
malaria.  In  such  cases,  where  do  the  germs  come  from  that  cause 
the  disease?  People  sometimes  have  chills  and  fever  in  the  winter 
or  spring  when  no  mosquitoes  are  flying.  Where  do  the  malaria 
germs  come  from  in  these  cases? 

When  persons  who  have  been  vaccinated  take  smallpox,  they 
usually  have  a  light  attack  of  the  disease.  Why  should  you  expect 
this  to  be  the  case  ?  Ask  a  physician  to  explain  to  you  the  Pasteur 
treatment  for  hydrophobia.  How  does  the  principle  underlying  this 
treatment  resemble  the  principle  on  which  vaccination  is  founded? 

With  a  microscope  examine  a  drop  of  dirty  water  for  protozoa. 


CHAPTER    XXIV 

DISEASES    CAUSED    BY    BACTERIA 

BACTERIA  are  so  extremely  small  that  millions  of  them 
have  plenty  of  room  to  swim  about  in  a  drop  of  water,  and 
a  drop  of  sour  milk  commonly  contains  about  fifty  million 
bacteria.  It  would  require  twenty-five  thousand  of-  them, 
placed  side  by  side,  to  make  a  row  an  inch  long.  Examined 
under  a  microscope  that  would  cause  a  man  to  appear  as 
high  as  Mount  Washington  or  Mount  Mitchell,  bacteria  look 
about  as  large  as  the  periods  and  commas  in  ordinary  print. 
So  exceedingly  small  are  these  little  plants  that  they  can 
pass  through  the  pores  •  in  a  brick  as  easily  as  a  man  passes 
through  the  doorway  of  a  house. 

Another  remarkable  thing  about  bacteria  is  their  power  of 
multiplication.  It  has  been  calculated  that  if  all  the  bacteria 
in  the  world  could  get  food,  warmth,  and  moisture  so  that 
they  could  multiply  as  fast  as  they  are  capable  of  doing,  in 
two  days  they  would  fill  all  the  oceans  and  cover  all  the  land 
fifty  feet  deep.  Fortunately  for  us,  most  of  them  are  held  in 
check  by  lack  of  the  right  conditions  for  growth.  Yet  they 
show  what  they  can  do  when  they  get  into  such  favorable 
places  as  warm  milk;  for  a  quart  of  milk,  before  it  sours  and 
thickens,  usually  contains  eight  or  nine  hundred  billions  of 
bacteria. 

The  Distribution  of  Bacteria.  Bacteria  are  everywhere 
about  us  —  in  the  water,  in  the  soil,  and  clinging  to  the  small 

303 


304  HUMAN  PHYSIOLOGY 

particles  of  matter  that  are  always  floating  about  in  the  air. 
About  three  million  bacteria  are  ordinarily  found  in  an  ounce 
of  cultivated  soil,  and  they  are  much  more  abundant  than 
this  in  the  earth  around  houses  and  barns.  The  water  from 
most  wells  contains  more  than  one  million  bacteria  to  the 
quart.  Millions  of  bacteria  are  always  growing  on  the  hu- 
man skin,  and  in  the  mouth,  the  intestine,  and  the  respiratory 
passages.  Some  kinds  of  bacteria  are  useful ;  most  kinds  are 
harmless,  and  to  them  we  pay  no  attention ;  but  a  few  kinds 
produce  toxins  in  the  human  body  that  cause  some  of  our 
worst  diseases. 

Shapes  of  Bacteria.     Bacteria  are  cylindrical,  spherical,  or 

spiral — shaped  like  a  firecracker,  a  marble,  or  a  corkscrew. 

^  The  cylindrical  bacteria  are  called 

S/      d^jp^^HRx  bacilli  (singular,    bacillus).     The 

C^  V— j^-^^V"^-^  cr^  \~\  i^fi  /~»o  1      rvo  /"»i~£n*i  o      o  t*£*     /"»r»llor1      /*o/*/*'» 


A  spherical  bacteria  are  called  cocci 
FIG.  141.  Bacteria.  A  is  a  ba-  (singular,  coccus),  and  the  spiral 
ciiius,  B  is  a  coccus,  and  c  is  a  forms  are  called  spirilla  (singular, 
spirillum<  spirillum}.  The  shapes  of  bac- 
teria have  nothing  to  do  with  the  diseases  which  bacteria 
cause,  but  often  give  a  convenient  way  of  distinguishing 
between  different  kinds. 


BACTERIAL   DISEASES   OF  THE   RESPIRATORY   ORGANS 

Diphtheria.  The  diphtheria  germ  grows  usually  in  the 
pharynx,  but  is  also  commonly  found  in  the  larynx  and 
mouth,  is  sometimes  found  on  the  lips  and  in  the  nose,  and 
may  grow  in  other  parts  of  the  body.  It  does  not  usually 
grow  outside  of  the  human  body,  but  it  can  remain  alive  for 
several  weeks  in  matter  that  has  come  from  the  throat  of 
a  diphtheria  patient.  On  slate  pencils  that  have  touched  the 


DISEASES   CAUSED   BY  BACTERIA  30$ 

lips  of  a  person  who  has  diphtheria,  living  diphtheria  bacilli 
have  been  found  for  several  days.  The  incubation  period 
of  the  disease  is  usually  from  two  to  seven  days,  but  may 
be  less. 

Sometimes  attacks  of  diphtheria  are  so  severe  that  death 
comes  in  a  day  or  two.     In  other  cases,  the  germs  make  only 
a  slight  growth  before  the  body  gets  the  upper  hand  of  them, 
and  the  attack  is  so  light  that  it  is  often  mis- 
taken for  a  simple  case  of  sore  throat.      In 
still  other  cases,  the  diphtheria  bacillus    lives        j 
;.n  the  throat  without  causing  illness  at    all.1        •  ms^a£ 
Where  the  germs  remain  in  the  throat  without        JT'**'  *& 
causing  sickness,  the  body  is  able  to  hold  them         FIG.  142.  The 
in  check  and  keep  them  from  making  enough      *Phtheria  baciu 
growth  to  harm  it,  but  is  not  able  to  kill  them 
out  entirely.     After  recovery  from  an  attack  of  diphtheria  it 
is  not  uncommon  for  virulent  germs  to  be  found  in  the  throat 
for  four  or  five  weeks,  and  in  one  case  they  were  found  eight 
months  after  recovery  from  the  disease.     The  disease  called 
membranous  croup  is  the  same  as  diphtheria. 

How  Diphtheria  is  contracted.  Diphtheria  is  usually  con- 
tracted by  inhaling  the  germs.  Frequently  germs  that  have 
been  coughed  out  into  the. air2  by  a  person  who  has  the  bacil- 
lus of  diphtheria  in  his  throat  are  inhaled.  Dried  sputum 

1  Most  healthy  persons  who  have  the  diphtheria  germs  in  their  throats  have 
been  about  some  one  who  is  suffering  from  the  disease. 

2  In  coughing,  sneezing,  laughing,  and  to  a  certain  extent  in  talking,  small 
droplets  of  liquid  are  sent  out  into  the  air.     These  may  fly  to  a  distance  of  three 
feet,  and  some  of  them  are  so  very  fine  that  they  are  said  to  float  in  the  air  for  as 
long  as  twenty  minutes.     When  a  person  is  suffering  from  a  disease  like  diphthe- 
ria, pneumonia,  or  consumption,  these  droplets  are  of  course  filled  with  the  germs 
of  the  disease.     One  should  not  stand  near  a  person  who  is  coughing,  and  a  sick 
person  should  hold  a  handkerchief  before  his  face  when  he  coughs. 


306   '  HUMAN  PHYSIOLOGY 

which  contains  diphtheria  germs  may  spread  the  disease  by 
being  blown  about  as  dust  and  inhaled.  The  germs  are 
almost  certain  to  get  on  the  handkerchiefs  and  hands  of 
persons  having  the  disease.  They  may  be  left  on  a  drinking 
cup  or  on  a  pencil,  on  a  toy  or  a  piece  of  candy  that  has 
been  handed  about  among  children,  and  in  many  other  ways 
they  may  be  transferred  from  one  person  to  another.  They 
sometimes  get  into  the  body  from  milk  (page  330)  and  they 
are  often  carried  by  flies  and  left  where  they  reach  the 
respiratory  passages. 

Quarantining  in  Cases  of  Diphtheria.  The  diphtheria  germ 
is  sometimes  found  in  the  throats  of  healthy  persons,  in  the 
throats  of  diphtheria  patients  who  have  long  since  recovered 
from  the  disease,  and  in  mild  diphtheria  cases  where  the  disease 
has  not  been  recognized.  Persons  are  therefore  going  about 
who  are  themselves  perfectly  well,  or  at  least  only  slightly  ill, 
but  who  nevertheless  carry  diphtheria  germs  that  are  exceed- 
ingly dangerous  to  others.  These  persons  usually  object  to 
being  quarantined,  and  health  officials  have  great  difficulty  in 
preventing  the  spread  of  diphtheria.  The  only  way  by  which 
the  disease  can  really  be  controlled  is  to  shut  up  in  quarantine 
every  one  who  has  virulent  diphtheria  germs  in  his  throat, 
whether  or  not  he  is  himself  ill.  This  often  involves  quaran- 
tining for  long  periods  of  time  both  diphtheria  patients  and 
members  of  families  in  which  there  is  diphtheria. 

Diphtheria  Toxin  and  Antitoxin.  The  diphtheria  germ  may 
cause  death  by  closing  the  throat,  but  usually  the  cause  of 
death  is  the  very  powerful  toxin  which  the  germ  produces. 
This  toxin  attacks  the  nervous  and  the  muscular  systems, 
and  the  direct  cause  of  death  often  is  that  the  nerve  and 
muscle  cells  of  the  heart  are  so  injured  that  the  heart  stops. 

We  have  already  studied  about  how,  when  germs  get  into 


DISEASES  CAUSED  BY  BACTERIA  307 

the  body,  the  body  begins  to  work  up  its  power  of  killing 
them.  So  when  toxin  is  produced  in  the  body,  the  body 
works  up  a  substance  called  antitoxin  that  neutralizes,  or 
destroys,  the  toxin.  If  the  body  can  produce  enough  anti- 
toxin to  keep  the  toxin  from  poisoning  the  cells,  the  germi- 
cidal  power  of  the  blood  will  rise,  and  finally  the  germs  will 
be  killed  out.  But  if  the  toxin  is  not  destroyed,  it  will  poison 
the  body  and  take  away  its  power  of  killing  germs,  the  bac- 
teria will  triumph,  and  death  will  come.  The  antitoxin  does 
not  kill  the  germs,  but  protects  the  body  from  the  toxin  until 
the  white  corpuscles  and  the  germicidal  substance  in  the  blood 
can  overcome  the  germs. 

The  Antitoxin  Treatment.  It  was  found  that  the  horse 
has  a  very  great  power  of  producing  antitoxin,  and  the  anti- 
toxin now  constantly  used  in  the  treatment  of  diphtheria  is 
secured  from  the  horse  in  the  following  way : 

Diphtheria  germs  are  placed  in  beef  broth,  where  they 
grow  and  multiply,  and  produce  great  amounts  of  toxin.  A 
little  of  this  toxin  is  then  injected  into  the  blood  of  a  horse, 
and  the  horse  works  up  antitoxin  to  destroy  it.  Then  a 
larger  dose  of  toxin  is  given  the  horse,  and  still  more  anti- 
toxin appears  in  the  blood.  This  is  kept  up  until  the  blood 
is  made  as  strong  in  antitoxin  as  possible.  Then  the  horse 
is  bled,  and  the  blood  allowed  to  coagulate,  or  clot.  The 
thin,  yellowish  serum  that  appears  around  the  clot  contains 
the  antitoxin,  and  it  is  this  which  is  placed  in  sealed  bottles 
and  sold  as  antitoxin  after  it  has  been  freed  from  certain 
slightly  injurious  substances  which  it  contains. 

When  a  person  has  diphtheria,  and  the  germs  begin  to 
manufacture  toxin  and  poison  the  cells,  some  of  the  antitoxin 
from  the  horse  is  injected  into  the  blood.  This  unites  with 
the  toxin  and  saves  the  body  cells  from  being  poisoned,  thus 


308  HUMAN  PHYSIOLOGY 

giving  the  body  time  to  kill  out  the  germs  and  so  to  stop  the 
disease.  When  antitoxin  is  used  in  the  early  stages  of  the 
disease,  the  death  rate  is  only  about  one  fourth  as  great  as 
when  it  is  not  used.  But  it  is  very  important  to  use  it  early, 
for  after  the  toxin  has  already  poisoned  and  destroyed  the 
cells,  it  is  too  late  for  the  antitoxin  to  be  used  with  much 
benefit.  It  is  useful,  however,  in  all  stages  of  the  disease, 
and  when  a  person  has  been  exposed  to  diphtheria  is  often 
given  as  a  preventive  of  the  disease. 

Pneumonia.     Pneumonia  is  caused  by  a  small  coccus  grow- 
ing in  the  lungs.     This  germ  grows  not  only  in  the  lungs  and 
.,....-.:£:£..  air  passages,  but  quite  frequently,  especially 

•^iN^--3i&.  m  children,  gets  into  the  tympanum  and 
•:^'^  :-  ^  %  •  causes  inflammation  of  the  middle  ear.]  It 
/:3^:?% v'-*  *+•:  may  also  cause  meningitis  (page  317),  and 

•:v^-;^>. :..••'  it  attacks  many  animals  as  well  as  man. 
FIG.  143.  The  pneu-  In  the  colder  parts  of  our  country  pneu- 
monia germ.  monia  causes  more  deaths  than  any  other 
disease  —  more  even  than  consumption.  The  germs  can  sur- 
vive more  drying  and  sunlight  than  diphtheria  germs,  and  are 
more  frequently  in  the  air.  They  are  scattered  about  in  the 
same  ways  that  diphtheria  germs  are  scattered,  for  the  sputum 
of  a  pneumonia  patient  is  filled  with  the  germs.  The  germi- 
cidal  substance  which  is  worked  up  by  the  body  to  kill  the 
pneumonia  germ  stays  in  the  blood  only  a  short  time,  and  a 
person  may  have  the  disease  again  and  again.  So  quickly 

1  Inflammation  of  the  middle  ear  is  caused  by  many  different  kinds  of  germs. 
It  is  very  serious,  for  incurable  deafness  will  follow  the  breaking  down  of  the  chain 
of  bones,  and  there  is  danger  of  the  inflammation  spreading.  Sometimes  the 
germs  get  into  the  cavities  that  are  in  the  bone  above  the  middle  ear  (Fig.  119), 
producing  the  disease  called  mastoidilis,  and  sometimes  they  work  through  into 
the  cranial  cavity  and  cause  meningitis.  Running  ears  and  other  diseases  of  the 
ear  from  which  children  especially  suffer  should  not  be  neglected, 


DISEASES   CAUSED   BY  BACTERIA  309 

indeed  does  this  germicidal  substance  disappear  from  the 
blood  that  the  patient  may  have  a  relapse  before  he  has 
completely  recovered  from  an  attack  of  the  disease. 

Preventing  Pneumonia.  It  is  not  advisable  to  expose  one's 
self  unnecessarily- to  pneumonia  germs,  for  the  germs  fresh 
from  a  pneumonia  patient  are  often  very  vigorous  and  power- 
ful in  producing  the  disease.  It  is  not  possible,  however,  to 
avoid  entirely  the  pneumonia  germ,  for  it  is  common  in  the 
air,  and  a  very  great  number  of  people  —  probably  more  than 
half  of  those  living  in  colder  climates  —  are  carrying  it  in 
their  throats.  All  of  us  are  sure  at  some  time  to  inhale  it, 
and  the  best  preventive  is  to  keep  up  the  health  when  pneu- 
monia weather  comes,  so  that  the  body  will  be  able  to  kill 
out  any  germs  that  may  find  their  way  to  the  lungs.  This 
is  done  by  avoiding  all  exposure  to  cold  and  wet,  avoiding 
alcoholic  drinks,  taking  plenty  of  sleep  and  exercise,  and 
spending  as  much  time  as  possible  in  the  fresh  air.  Any- 
thing that  builds  up  the  general  health  is  a  safeguard  against 
pneumonia,  and  anything  that  weakens  the  body  may  bring  on 
the  disease,  for  the  pneumonia  germ  is  already  in  the  throats 
of  millions  of  people,  waiting  for  something  to  lower  the  germi- 
cidal power  of  the  body  so  that  it  can  grow  unchecked  and 
cause  the  disease.  An  important  safeguard  is  to  destroy 
carefully  the  sputum  from  a  pneumonia  patient  (page  336). 

Influenza  or  Grip.  Influenza  is  caused  by  a  very  small 
bacillus  that  grows  in  the  respiratory  passages.  The  grip 
bacilli  spread  in  much  the  same  ways  as  do  the  germs  of 
diphtheria  and  pneumonia,  but  the  grip  germs  die  much 
more  quickly  from  drying  than  either  of  the  others.  They 
linger  for  a  long  time  —  sometimes  for  more  than  a  year  — 
in  the  nose  and  bronchial  tubes  of  those  who  have  had  the 
disease,  and  are  often  found  in  those  who  have  bronchitis 


310  HUMAN  PHYSIOLOGY 

• 
and  consumption.     No  attempt  is  made  by  public  officials  to 

quarantine  grip  patients;  in  families  there  is  usually  little 
care  taken  to  keep  the  germ  from  those  who  have  not  taken 
the  disease;  and  grip  germs  are,  therefore,  spread  everywhere. 
In  grip  epidemics  a  large  portion  of  the  population  suffers, 
one  third  of  all  the  people  in  Chicago  having 
the  disease  at  one  time  in  January,  1908. 

The  grip  germ  produces  a  toxin  that  has  a 
very  profound  effect  on  the  body.  It  does  not 
FIG.  144.  The  in-  poison  the  body  so  acutely  as  the  diphtheria 
fluenza  bacillus.  toxin  does,  but  causes  a  weakness  and  a  de- 
pression that  often  last  for  months.  Grip  also  often  brings  on 
other  troubles,  such  as  pneumonia,  eye  and  ear  diseases,  and 
colds,  and  it  frequently  leaves  parts  of  the  body,  like  the  kid- 
neys, the  stomach,  or  the  nervous  system,  in  a  weakened  and 
diseased  condition.  Because  of  these  after-effects,  because 
it  attacks  so  many  people,  and  because  one  may  have  grip 
again  and  again,  influenza  is  a  much-dreaded  disease. 

Catarrh  and  Colds.  In  catarrh  and  colds  many  kinds  of 
germs  grow  in  the  respiratory  passages,  and  it  is  not  always 
easy  to  tell  which  one  is  causing  the  trouble.  It  seems  prob- 
able that  these  diseases  are  caused,  sometimes  at  least,  by  the 
same  germs  that  at  other  times  cause  pneumonia  and  influ- 
enza. This  would  not  be  so  strange  as  it  may  seem,  for  we 
know  of  other  instances  of  one  germ  causing  several  diseases 
that  seem  to  be  very  different  (page  311).  It  is  practically 
certain  that  colds  are  caused  by  germs,  for  colds  often  run  in 
epidemics,  and  epidemics  can  be  explained  only  on  the  theory 
that  a  germ  that  is  transferred  from  one  person  to  another  is 
causing  the  disease. 

Whooping-Cough.  Whooping-cough  is  undoubtedly  a  germ 
disease,  but  nothing  is  known  of  the  germ  that  causes  it. 


D/S EASES  CAUSED  BY  BACTERIA  311 

Consumption.     Consumption  is  so  important  a  disease  that 
it  will  be  discussed  in  a  separate  chapter  (chapter  XXVI). 


DISEASES   CAUSED    BY   BACTERIA  THAT   ENTER  THE   BODY 
THROUGH   THE   SKIN 

The  Pus-forming  Bacteria.  Several  different  kinds  of 
bacteria  are  included  in  this  group.  They  are  found  in  earth 
around  the  habitations  of  men 
and  animals  and  in  polluted 
water,  and  are  always  found 
on  the  human  skin,  where 
they  feed  on  the  dead  cells 
and  other  matter  on  the  skin. 
When  they  grow  in  the  tissues, 
they  cause  inflammation  and 
form  pusy  or  the  thick  liquid 
matter  that  is  found  in  boils 
and  infected  wounds. 

Diseases  caused  by  the  Pus- 
forming  Bacteria.  The  pus-forming  bacteria  cause  boils, 
carbuncles,  erysipelas,  blood  poisoning,  and  inflammation  in 
wounds  and  sores.  They  may  also  cause  inflammation  in  the 
internal  parts  of  the  body.  Tonsilitis  and  appendicitis  are 
usually  caused  by  these  germs,  and  meningitis  maybe  caused 
by  them.  It  thus  appears  that  the  same  germ  that  makes  a 
wide-spreading  growth  in  the  skin  and  causes  erysipelas,  can 
make  a  deep,  localized  growth  and  cause  a  boil  or  carbuncle, 
spread  through  all  the  body  and  bring  on  blood  poisoning,  or 
produce  spinal  meningitis  by  growing  in  the  membranes  and 
fluids  around  the  brain  and  cord.  The  pus-forming  germs 
found  in  cases  of  erysipelas  and  abscesses  are  often  very 
malignant,  and  care  should  be  used  to  prevent  their  spread. 


FIG.  145.  Three  pus-forming  bac- 
teria. A  causes  the  bluish-green  pus 
sometimes  found  in  wounds;  B  is  the 
most  common  cause  of  boils;  and  C 
causes  erysipelas  and  often  is  the  cause 
of  boils  and  of  blood  poisoning. 


312  HUMAN  PHYSIOLOGY 

The  Pus-forming  Germs  Injurious  to  the  Body.  A  strange 
idea  that  is  very  prevalent  is  that  boils  are  beneficial  to  us. 
Probably  this  belief  arises  from  the  fact  that  so  much 
offensive  matter  comes  from  a  boil.  It  is  exceedingly  im- 
portant to  open  up  infected  wounds,  boils,  and  carbuncles, 
and  get  the  matter  in  them  out  of  the  body,  for  it  is  injurious 
and  dangerous  to  allow  it  to  be  carried  through  the  body  by 
the  blood.  The  pus,  however,  is  composed  chiefly  of  germs, 
dead  tissue  cells,  and  dead  white  corpuscles  which  the  germs 
have  killed.  It  no  more  benefits  the  body  to  have  pus- 
forming  germs  kill  patches  of  the  tissue  and  poison  the 
whole  system  with  their  toxins  than  it  benefits  the  body  to 
have  diphtheria,  typhoid,  or  any  other  disease  germs  in  it. 

Care  of  Wounds.  For  our  protection  against  pus-forming 
germs,  it  is  very  important  to  know  how  to  care  for  small 
wounds.  If  the  wound  has  been  made  by  a  clean  instrument, 
and  bleeds  freely,  the  blood  will  wash  the  germs  outward, 
and  by  its  germicidal  power  will  probably  kill  any  bacteria 
remaining  in  the  wound.  In  such  a  case,  the  best  thing  is  to 
tie  the  wound  up  "  in  the  blood,"  and  not  open  it  until  it 
is  healed,  unless  inflammation  sets  in.  A  good  plan  is  to 
wrap  the  wounded  part  in  a  thin,  clean  inner  cloth,  and  out- 
side of  this  tie  a  second  cloth.  The  outer  cloth  can  be  changed 
from  time  to  time  when  it  becomes  soiled,  while  the  innei 
cloth  is  left  undisturbed  to  keep  germs  from  getting  into  the 
wound. 

When  a  wound  has  been  made  with  anything  unclean,  it 
should  be  washed  with  a  disinfectant  (page  335)  to  kill  germs 
in  it,  before  it  is  tied  up.  After  being  bandaged,  a  wound 
should  be  carefully  watched,  and  if  pain,  redness,  and  swelling 
show  that  germs  have  got  into  it,  it  should  be  opened  at 
once  and  disinfected.  A  salve  containing  carbolic  acid  is 


DISEASES   CAUSED  BY  BACTERIA  313 

very  useful  in  dressing  small  wounds  and  sores,  because  the 
carbolic  acid  kills  germs.  Turpentine  is  an  excellent  agent 
with  which  to  treat  a  wound,  and  one  that  is  often  at  hand. 

Rheumatism.  Acute  rheumatism  is  a  germ  disease.  Some 
think  that  it  is  caused  by  pus-forming  bacteria  growing  in  the 
joints,  and  others  hold  that  it  is  caused  by  a  very  tiny  germ 
of  its  own.  When  this  disease  attacks  the  valves  of  the 
heart,  it  is  often  fatal. 

Tetanus  (lockjaw).     Tetanus  is  caused  by  a  bacillus  that  is 
commonly  found  in  the  earth  about  dooryards  and  gardens, 
in  the  dust  of  streets,  and  in  great  abundance 
about  stables  where  horses  are  kept.     It  affects    «=»  j&  ^ 
chiefly    man  and  the  horse  and  gets   into    the 
body  through   wounds,   often   through   wounds 
so    small    and    insignificant   that    no    attention 
is  paid  to  them.      The  tetanus  germ  by  itself      FIG.      146. 
cannot   grow    except  when  it  is  shut  off  from  The  bacillus  of 

tetanus. 

the   air.     With  other  germs,    however,  it   can 
grow  in  an  open  wound. 

The  tetanus  bacillus  grows  especially  in  wounds  made  by 
unclean  instruments,  because  such  wounds  are  likely  to  be 
infected  with  this  germ,  and  because  pus-forming  germs  and 
particles  of  dirt  are  left  in  such  wounds.  It  grows  best  of 
all  in  small,  deep  wounds  like  those  caused  by  an  unclean 
nail,  because  wounds  of  this  kind  readily  close  over  and 
leave  the  tetanus  germ  with  other  germs  and  foreign  matter 
buried  deep  in  the  flesh  and  away  from  the  air.  The  percus- 
sion caps  used  on  toy  pistols  also  make  dangerous  wounds. 
The  germs  are  in  the  dust  on  the  skin,  and  the  very  small, 
sharp,  flying  particles  of  the  caps  cut  deep  into  the  flesh  and 
drive  down  tetanus  germs  along  with  other  bacteria  and  dust. 

The  bacillus  of  tetanus  is  so  common  that  it  undoubtedly 


314  HUMAN  PHYSIOLOGY 

gets  into  many  wounds  in  which  it  never  grows,  but  it  is 
always  wise  to  look  after  and  protect  every  wound.  Wounds 
made  by  unclean  instruments  should  be  carefully  sterilized, 
and  wounds  on  the  feet  of  barefooted  children  should  re- 
ceive special  attention,  because  these  come  in  contact  with 
the  earth  and  are  exposed  to  infection.  Wounds  of  a  kind 
that  are  especially  liable  to  cause  the  development  of  the 
disease  should  be  looked  after  by  a  physician. 

The  Toxin  of  Tetanus.  The  tetanus  germ  makes  only  a 
very  slight  growth  in  the  body,  but  it  produces  a  toxin  of  tre- 
mendous power.  This  toxin  for  man  is  a  poison  nineteen 
times  as  strong  as  dried  cobra  venom,  and  two  hundred  and 
fifty  times  as  strong  as  strychnin.  It  produces  its  effects 
by  poisoning  the  nervous  system,  and  through  this  so  affects 
the  muscles  that  they  are  all  thrown  into  contraction.  The 
muscles  of  the  jaw,  esophagus,  and  neck  are  often  affected 
before  the  other  muscles  in  tetanus. 

Tetanus  Antitoxin.  An  antitoxin  for  tetanus  has  been  pre- 
pared, but  this  is  successful  only  when  used  in  large  doses 
very  soon  after  the  disease  develops.  It  is  very  useful,  how- 
ever, in  preventing  tetanus,  and  when  a  person  has  received 
a  wound  that  is  likely  to  bring  on  this  disease,  many  physi- 
cians make  a  regular  practice  of  giving  a  dose  of  tetanus  anti- 
toxin to  keep  the  disease  from  developing. 

Leprosy.  Leprosy  is  caused  by  a  slow-growing  bacterium, 
similar  in  some  ways  to  the  tuberculosis  germ.  It  produces 
little  toxin,  and  may  exist  in  great  numbers  in  the  tissues  of 
the  body  for  years  before  death  results.  There  is  no  cure  for 
leprosy,  and  it  is  slightly  contagious,  though  not  so  conta- 
gious as  consumption. 

Bubonic  Plague.  Bubonic  plague  is  the  disease  that  was 
called  the  Black  Death  in  the  Middle  Ages.  In  1907  there 


DISEASES  CAUSED  BY  BACTERIA  315 

were  over  a  million  cases  of  plague  and  860,000  deaths  from 
it  in  India.  It  is  caused  by  a  bacillus  that  gets  into  the  body 
through  wounds  or  through  the  bites  of  fleas,  lice,  or  other 
insects.  It  produces  a  violent  toxin,  and  about  85  per  cent 
of  those  attacked  by  it  die.  This  disease  also  attacks  rats 
and  mice,  and  is  spread  from  house  to  house,  or  from  one 

country  to  another  by  rats  and  the  fleas  which  the  rats  carry. 

» 

BACTERIAL   DISEASES  OF   THE  ALIMENTARY   CANAL 

Typhoid  Fever.  This  disease  is  caused  by  a  bacillus  that 
is  taken  into  the  body  through  the  mouth,  usually  in  water  or 
food.  It  grows  most  commonly  in  the 
wall  of  the  small  intestine,  but  is  some- 
times found  in  other  parts  of  the  body. 
Sometimes  an  attack  of  typhoid  fever  is  so 
light  that  the  patient  does  not  realize  that 
there  is  much  the  matter  with  him.  Usu- 

FiG.  147.     The  ba- 

ally  it  is  a  very  severe  disease,  and  often  Cnius  of  typhoid  fever, 
leaves  the  sufferer  weakened  in  some  or-  This  germ  is  fitted  for 

f        ,.r          ^,  .  r  ,1  life  in  the  water  and 

gan  for  life.     The  excretions  from  the  in-     swims  active]y 
testines  and  kidneys  of  a  typhoid  patient 
are  filled  with  the  germs.1     These  germs  can  grow  in  water 
and  in  refuse  matter  outside  of   the  body,  but  if  they   are 
dried,  they  die  in  a  very  short  time. 

How  Typhoid  is  contracted.  Since  the  typhoid  germ  dies 
from  drying,  it  is  not  carried  about  in  the  air,  but  must  get 

1  About  one  person  in  every  thirty  who  has  typhoid  fever  carries  the  typhoid 
bacillus  through  life.  The  germs  remain  in  the  gall  bladder  and  intestine  with- 
out seeming  to  affect  the  person  in  whom  they  are  growing.  A  cook  in  New 
York  City  infected  twenty-six  persons  in  a  period  of  five  years,  and  the  germs 
have  been  found  in  the  excretions  from  the  body  forty-two  years  after  recovery 
from  the  disease. 


316  HUMAN  PHYSIOLOGY 

to  the  mouth  without  being  dried  out.  Persons  in  the  same 
house  with  a  typhoid  patient  may  contract  the  disease  from 
the  dishes,  by  getting  the  germs  on  the  hands,  from  han- 
dling the  bedding,  or  in  any  of  the  many  ways  by  which  it  is 
possible  for  such  small  bodies  as  bacteria  to  be  carried  about. 
Flies  will  carry  the  germs  about  in  great  numbers,  if  all 
wastes  from  typhoid  patients  are  not  carefully  destroyed. 
Occasionally  the  germ  is  in  oysters  that  have  been  grown  in 
polluted  waters,  and  for  this  reason,  cooked  oysters  are  safer 
than  raw  oysters.  In  a  large  number  of  cases,  the  typhoid 
germ  has  been  carried  in  milk  where  some  one  having  the 
disease  had  prepared  or  handled  the  milk,1  or  where  the  milk 
vessels  had  been  washed  in  water  containing  the  germs. 
If  a  single  typhoid  germ  should  get  into  a  can  of  milk,  it 
could  produce  thousands  or  perhaps  millions  of  germs  before 
the  milk  was  used,  so  the  milk  supply  must  be  carefully 
watched.  In  the  majority  of  cases,  however, 
typhoid  is  contracted  direct  from  water.  In 
the  next  chapter  we  shall  discuss  the  subject 
of  disease  germs  in  drinking  water. 

Cholera.     Cholera  is  caused  by  a  germ  that 
The      grows  witn  gr^at    rapidity  in    the   intestines, 
cholera  germ.       and  produces  a  strong  toxin,  sometimes  causing 
death  within  a  few  hours.      Like  the  typhoid 
germ,  it  gets  into  the  alimentary  canal  through  water  and  foods. 
Other  Bacterial  Diseases  of  the  Alimentary  Canal.     There 
is  a  group  of  germs  closely  related  to  the  typhoid  germ  that 
cause  intestinal  diseases.     The  worst  of  these  are  the  germs 
that  cause  so  much  sickness  among  small  children  during  the 
summer  months  (Appendix  B). 

1  In  the  spring  of  1908  one  milkman  in  Boston  who  was  suffering  from  typhoid 
caused  an  epidemic  of  about  400  cases. 


DISEASES  CAUSED  BY  BACTERIA  317 


OTHER   BACTERIAL   DISEASES 

Epidemic  cerebro-spinal  meningitis  is  caused  by  a  germ  that 
grows  in  the  membranes  and  fluid  around  the  brain  and  spinal 
cord.  The  germ  is  found  in  the  nasal  secretions 
of  those  suffering  from  the  disease.  It  is  thought 
that  spinal  meningitis  is  contracted  by  inhaling 
the  germ  into  the  nose,  whence  it  finds  its  way 
to  the  brain.  The  disease  is  contagious  and  care 

should  be  used  to  prevent  its  spread.    The  pneu- 

FIG.     149. 
monia  germ,  the  influenza  germ,  the  germ  of     The  germ    of 

tuberculosis,  and  one  of  the  pus-forming  germs     cerebro- spinal 
may  also  grow  around  the  brain  and  cord  and 
cause  meningitis,  but  the  common  contagious  form  of  the  dis- 
.  ..... j-.      ease  is  caused  by  the  germ  shown  in  Figure  149. 

•>  /i-fy  ^ne  f°rm  °f  sore  eyes  *s  caused  by  a  bac- 

/••/:v tfi^     terium.     The  germs  are  carried  by  flies  and 

'''•*f*.:'^fiS'=      may  be  wiped  on  books,  doorknobs,  or  any- 

'**«*^^      thing    which    a    sufferer    from    the    disease 

touches.     Children  with   this  disease   should 

FIG.  150.  The      not  be  allowed  to  attend  school,  for  it  is  highly 

bacillus  that  .  * 

causes      conta-      contagious.     It  is  never  quite  safe   to   wash 
gious  sore  eyes.      the  eyes  in  a  public  basin,  or  to  wipe  them 

on  a  towel  that  the  public  has  used. 

Yellow  fever,  chicken  pox,  mumps,  measles,  and  German 
measles  are  certainly  germ  diseases,  but  the  germs  that  cause 
them  have  not  been  discovered.1  Many  tropical  diseases  are 
due  to  either  bacteria  or  protozoa. 

1  The  incubation  periods  of  some  of  the  more  common  infectious  diseases  are 
as  follows :  chicken  pox,  usually  13  to  14  clays,  but  may  be  18  or  19  days;  mumps, 
13  to  21  days,  though  it  may  be  shorter;  measles,  about  8  days;  German  measles, 
from  2  103  weeks;  scarlet  fever,  2  to  5  days;  whooping-cough,  about  6  days. 


HUMAN  PHYSIOLOGY 


Bacteria  affecting  Animals.  Among  bacterial  diseases  of 
animals  are  hog  and  chicken  cholera,  distemper  and  glanders 

in  horses,  blackleg  in  cattle,  an  in- 
testinal disease  of  parrots,  and  many 
other  animal  diseases  that  we  cannot 
mention  here.  The  germs  of  the 
parrot  disease,  when  inhaled  by  man, 
produce  a  very  severe  form  of  pneu- 
monia, and  the  glanders  germ  attacks 
man  and  is  often  fatal  to  him. 

Diseases  caused  by  Other  Organ- 
isms. Many  diseases  of  plants 
(rusts,  smuts,  mildews,  rots,  etc.)  are 
caused  by  fungi  that  are  related  to 
the  molds  and  mildews.  These  are 
much  larger  than  bacteria,  their 
bodies  being  composed  of  long, 
thread-like  filaments.  A  few  of 
these  fungi  attack  man,  a  number 
of  them  entering  the  hair  follicles 
and  growing  in  the  skin.  Among 
the  diseases  caused  by  them  are  ring- 
worm, barber's  itch,  and  in  tropical 

countries,  an  itch  which  attacks  any  part  of  the  body.  Thrush, 
which  is  found  in  the  mouths  of  young  babies,  is  also  due  to  a 
fungus,  and  a  few  kinds  of  yeasts  occasionally  attack  the 
human  body. 

QUESTIONS 

Give  some  facts  that  show  the  extreme  smallness  of  bacteria. 
Where  are  bacteria  found  ?  What  shapes  have  they  ? 

Where  does  the  bacillus  of  diphtheria  grow?  How  long  can  the 
germ  remain  alive  outside  the  body?  What  is  the  incubation  period 


FIG.  151.    The  fungus  that 
causes  ringworm. 


DISEASES   CAUSED   BY  BACTERIA  319 

of  diphtheria?  How  is  it  contracted?  How  strict  a  quarantine  is 
necessary  to  control  diphtheria?  How  does  diphtheria  cause  death? 
What  is  antitoxin  ?  Explain  the  antitoxin  treatment  for  diphtheria. 
Why  should  the  antitoxin  be  used  in  the  early  stages  of  the  disease? 

In  what  parts  of  the  body  does  the  pneumonia  germ  grow?  How 
is  the  germ  transferred  from  one  person  to  another?  Give  two  ways 
by  which  the  disease  may  be  in  a  measure  prevented.  Where  does 
the  grip  germ  grow  ?  Why  is  grip  a  dreaded  disease  ?  By  what  germs 
are  catarrh  and  colds  perhaps  caused  ?  Why  do  we  suppose  that  colds 
are  germ  diseases? 

Name  some  of  the  diseases  caused  by  pus-forming  germs.  Of  what 
is  pus  composed?  How  should  a  wound  made  by  anything  clean  be 
treated?  a  wound  made  by  anything  unclean  ? 

Where  is  the  tetanus  bacillus  found?  Under  what  conditions  can 
it  grow  and  under  what  conditions  can  it  not  grow?  What  kind  of 
wounds  are  especially  dangerous?  How  does  the  tetanus  germ  injure 
the  body?  What  germ  does  the  leprosy  bacillus  resemble?  How  is 
plague  spread? 

How  does  the  typhoid  germ  enter  the  body?  What  part  of  the 
body  does  it  usually  attack?  What  excretions  from  a  typhoid 
patient  contain  the  germs?  Name  some  of  the  ways  typhoid  fever 
may  be  contracted.  How  does  the  cholera  germ  enter  the  body? 

By  what  germs  may  cerebro-spinal  meningitis  be  caused  ?  Where 
do  the  germs  grow  in  this  disease?  In  what  secretion  of  the  patient 
is  the  germ  found  ?  How  does  the  germ  probably  enter  the  body  ? 

How  may  the  germ  that  causes  sore  eyes  be  spread  ?  Name  other 
germ  diseases  ;  some  germ  diseases  of  animals  ;  some  diseases  caused 
by  larger  fungi. 

When  one  has  been  infected  with  diphtheria  or  tetanus  germs, 
antitoxin  helps  to  keep  the  disease  from  developing.  How  does  it 
do  this?  Are  typhoid  germs  killed  by  freezing  them  in  ice? 


CHAPTER   XXV 

PREVENTING  THE  SPREAD   OF  DISEASE  GERMS 

AFTER  most  kinds  of  disease  germs  begin  their  growth  in 
the  body,  medicines  are  of  very  little  use  except  to  keep  up  the 
body  strength.  In  our  warfare  with  germs,  we  must  there- 
fore depend  chiefly  either  on  keeping  the  germs  oat  of  the 
body,  or  on  the  natural  power  of  the  body  to  kill  them  after 
they  enter  it.  Keeping  up  the  germicidal  power  of  the  body, 
and  preventing  the  germs  of  infectious  diseases  from  being 
scattered  about,  are,  therefore,  the  most  important  points  in 
the  prevention  of  disease.  In  a  former  chapter  (page  290) 
we  have  discussed  the  necessity  of  keeping  up  the  resist- 
ance of  the  body  to  germs.  We  shall  now  study  the  best 
methods  of  keeping  the  germs  that  come  from  the  bodies 
of  sick  persons  from  being  spread  abroad. 

DANGERS  FROM  INSECTS 

Fleas  spread  the  germs  of  plague ;  mosquitoes  carry  many 
diseases ;  the  house-fly  is  a  great  carrier  of  germs ;  and  ticks 
and  certain  tropical  flies  are  known  to  carry  disease. 
The  bedbug  also  is  suspected  of  being  responsible  for  the 
spread  of  certain  diseases.  Any  insect  that  bites  us  has  an 
excellent  opportunity  to  introduce  germs  into  the  body,  and 
any  insect  that  crawls  over  our  food,  as  do  flies  and  cock- 
roaches, may  easily  spread  the  germs  of  many  diseases.  We 
shall  do  well,  therefore,  to  guard  ourselves  as  much  as 
possible  from  insects. 

320 


PREVENTING   THE  SPREAD    OF  DISEASE   GERMS     $21 


Mosquitoes.  The. mosquito,  more  than  any  other  one  agency, 
has  driven  man  from  the  warmer  and  more  fertile  portions 
of  the  earth  to  the  colder  and  more  barren  regions.  Not 
only  does  it  carry  the 'germs  of  malaria,  but  it  carries  yellow 
fever  and  dengue,  or  "breakbone  fever,"  a  disease  com- 
mon in  the  tropics  and  found  to  a  certain  extent,  in  some 
of  our  Southern  states.  The  germs  of  several  diseases  of  man 
not  found  in  our  country,  and  of  certain  diseases  of  birds, 


FlG.  1-2.  The  life  history  of  the  mosquito.  A  is  the  malaria-carrying  mosquito 
(Anopheles),  and  B,  the  common  mosquito  (Culex).  a  is  the  eggs;  b,  the  wriggler ; 
c,  the  tunbler ;  and  d,  the  adult  mosquito. 

are  also  carried  by  mosquitoes.  Where  it  is  possible  to 
do  so,  the  best  way  to  end  these  diseases  is  to  destroy  the 
mosquitoes.  To  work  at  this  intelligently  it  is  necessary 
first  to  know  the  life  history  of  the  mosquito. 

The  Life  History  of  the  Mosquito.  The  mosquito  lays  its 
eggs  on  water.  In  about  a  day  the  egg  hatches  into  a  wrig- 
gler that  swims  actively  about,  feeding  on  protozoa  and  other 
small  animals  that  are  in  the  water.  The  wriggler  takes  in 
air  through  a  breathing  tube,  which  it  thrusts  out  through  the 
surface  of  the  water  to  the  air,  as  shown  in  Figure  152. 

In  from  seven  to  fourteen  days  the  wriggler  changes  its 


322  HUMAN  PHYSIOLOGY 

form.  The  head  and  the  fore  part  of  the  body  become  much 
heavier,  and  the  breathing  tubes  shift  to  the  back  of  the  body. 
In  this  stage  it  is  called  a  tumbler,  because  instead  of  wrig- 
gling as  it  swims,  it  tumbles  over  and  over.  In  from  two  to 
five  days  —  ten  to  twenty  days  from  the  time  the  egg  was 
laid  —  the  tumbler  splits  down  the  back,  and  the  adult 
mosquito  comes  out  and  flies  away.  How  long  a  mosquito 
lives  in  the  adult  form  is  not  known,  but  one  has  been  kept 


FlG.  153.     A  is  the  malaria  mosquito  (Anopheles)  and  B  is  the  common  mosquito 

(Culex). 

for  seventy-six  days,  and  enough  of  them  always  live  through 
the  winter  to  furnish  a  plentiful  supply  for  the  next  summer.- 
Anopheles.  The  kind  of  mosquito  that  carries  the  germ 
of  malaria  is  called  Anopheles.  It  is  a  small,  almost  silent 
mosquito,  that  does  most  of  its  biting  in  the  early  part  of  the 
night.  It  can  readily  be  distinguished  from  other  mosquitoes 
by  the  black  spots  on  its  wings,  and  by  its  habit  of  elevating 
the  back  part  of  the  body,  or  standing  up  on  its  head,  when 
sitting  and  biting.  The  wriggler  of  Anopheles  can  be  dis- 
tinguished from  the  wriggler  of  other  mosquitoes  by  its 
position  while  breathing.  The  Anopheles  wriggler  lies 
almost  parallel  to  the  surface  of  the  water  (Fig.  152  A\  and 
the  other  wrigglers  take  a  position  almost  perpendicular  to 
the  surface  of  the  water  (Fig.  152  B). 


PREVENTING   THE  SPREAD   OF  DISEASE   GERMS     323 

Other  mosquitoes  are  often  carried  considerable  distances 
by  the  wind,  but  the  Anopheles  has  a  habit  of  clinging  to 
weeds,  shrubs,  and  bushes  when  the  wind  blows,  and  is 
not  often  found  far  from  the  place  where  it  is  hatched.  The 
mosquitoes  that  give  people  malaria  are  usually  raised  by 
those  same  people,  or  by  their  near  neighbors. 

How  to  destroy  Mosquitoes.  The  first  thing  in  the  fight 
with  mosquitoes  is  to  deprive  them  of  breeding  places  near 
human  dwellings.  An  old  fruit  can  may  catch  and  hold 
enough  rain  water  to  breed  a  large  number  of  mosquitoes ; 
in  the  course  of  a  summer,  an  almost  unlimited  number  can 
come  from  a  water  barrel  or  an  open  cistern ;  and  an  un- 
drained  ditch  by  the  roadside  may  supply  enough  mos- 
quitoes to  torment  and  infect  with  malaria  all  the  people  in 
the  vicinity. 

Old  cans  and  pans  should  be  cleared  away  ;  water  barrels, 
tanks,  and  cisterns  should  be  screened  so  that  the  mosquitoes 
cannot  get  to  them  to  lay  their  eggs;  sagging  eave  troughs 
should  be  braced  up  so  that  no  water  will  stand  in  them,  for 
wrigglers  may  start  here  in  a  very  small  quantity  of  water 
and  be  washed  down  into  the  cistern,  where  they  will  com- 
plete their  development.  All  pools  and  puddles  about  houses 
should  be  drained,  and  weeds  and  shrubbery  in  which  the 
mosquitoes  can  find  a  dark,  cool  place  to  hide  during  the  hot 
part  of  the  day,  or  when  the  wind  blows,  should  be  cut  down. 

When  pools  of  water  cannot  be  drained,  it  is  an  easy 
matter  to  kill  all  young  mosquitoes  in  them  by  pouring  a  little 
kerosene  on  the  water.  This  forms  a  film  over  the  water, 
shutting  the  wrigglers  off  from  the  air,  and  killing  them  in  a 
few  minutes.  If  the  kerosene  is  washed  away  by  rains,  it 
must  be  renewed  within  ten  days,  for  this  is  about  the  time 
it  takes  a  mosquito  egg  to  grow  into  a  mosquito.  Minnows 

I 


324  HUMAN  PHYSIOLOGY 

and  tadpoles  feed  on  the  mosquito  wrigglers,  so  by  introduc- 
ing these  into  a  pond,  the  number  of  mosquitoes  that  breed 
there  may  be  greatly  lessened. 

The  work  of  destroying  mosquitoes  in  cities  and  towns 
must  be  taken  up  by  public  officials  who  have  authority 
to  compel  every  one  to  put  his  premises  in  sanitary  con- 
dition. Otherwise  enough  persons  will  keep  breeding  places 
for  mosquitoes  to  infect  the  whole  town.  When  the  work 
is  undertaken  in  this  way,  it  is  a  simple  and  not  at  all  expen- 
sive matter  entirely  to  eradicate  mosquitoes  and  malaria  from 
a  town,  as  has  been  done  in  many  places. 

The  Danger  of  Flies.     There  is  a  belief  among  some  people 
that  flies  are  useful  scavengers.     No  greater  mistake  could 
be  made,  for  they  light  in  and  walk  over 
all  manner  of  unclean  matter,  and  then  fly 
into  the  house  and  spread  germs  and  un- 
cleanness  over  dishes,  food,  milk  vessels, 
and  everything  that  they  come  in  contact 
with.1     Not  only  do  they  carry  germs  on 
their   feet,  but  when   a    fly    feeds  on  the 
FIG.  154.    The  foot     Sputum  of   a   consumptive    or  the  wastes 

of  a  fly.     A  fly  usually          r 

has  great  numbers  of  from  a  typhoid  patient,  the  germs  of  these 
germs  clinging  to  its  diseases  are  found  alive  in  the  matter  from 

its  alimentary  canal. 

Flies  may  carry  almost  any  kind  of  disease  germs,  so  a 
sick  person  should  be  carefully  screened  away  from  them,  and 
all  matter  from  the  body  of  a  sick  person  should  be  destroyed 
immediately.  Otherwise,  every  one  in  the  vicinity  is  in 
danger  of  contracting  the  disease  through  the  flies. 

1 A  fly  was  caught  and  made  to  walk  over  a  plate  of  gelatine  for  two  minutes. 
In  that  time  it  left  289  germs  in  the  gelatine.  Another  fly  has  been  reported  as 
having  100,000  germs  on  its  legs. 


PREVENTING   THE  SPREAD   OF  DISEASE  GERMS    325 


FIG.  155.  The  house-fly.  A  is  the 
egg  which  is  laid  in  manure ;  B  is  the 
larva  or  maggot ;  C  is  the  pupa  or  rest- 
ing state ;  and  D  is  the  adult  fly. 


Keeping  Free  from  Flies.  It  is  possible  to  do  much  in 
the  way  of  avoiding  danger  from  flies  by  using  screens  and 
flypaper,  by  covering  food  and 
dishes,  and  by  removing  all 
materials  that  attract  them  to 
the  house.  A  far  easier  and 
more  effective  way  is  to  re- 
move the  breeding  places  of 
the  flies.  The  egg  of  the 
house-fly  is  laid  in  manure 
about  stables,  or  in  the  matter 
in  water-closets.  In  a  day  or 
less,  this  hatches  into  a  small, 
white,  footless  maggot,  which  in  nine  or  ten  days  from  the 
time  the  egg  was  laid  changes  into  the  adult  fly. 

It  is  estimated  that  in  one  summer  300  flies  may  hatch 
in  a  cubic  inch  of  manure,  and  if  the  breeding  places  of  the 
flies  are  left  undisturbed,  they  will  hatch  faster  than  it  is 
possible  to  kill  them.  It  is  a  simple  matter,  however,  to 
stop  their  increase  by  removing,  once  a  week,  all  matter  in 
which  they  breed,  burying  it,  or  spreading  it  on  the  fields 
where  it  will  dry  and  the  eggs  and  young  will  be  killed. 

Flies  can  also  be  prevented  from  hatching  by  thorough 
sprinkling  of  the  matter  in  which  they  breed  with  water  con- 
taining a  little  petroleum,  or  by  covering  it  with  lime,  or  by 
keeping  it  covered  so  that  the  adult  flies  cannot  get  to  it  to 
lay  the  eggs. 

DANGER  FROM   DUST 

In  a  cubic  yard  of  ordinary  air,  there  are  from  a  hundred 
to  a  thousand  bacteria.  These  bacteria  are  attached  to  float- 
ing particles  of  matter  of  one  kind  or  another.  Air  that 


326  HUMAN  PHYSIOLOGY 

is  absolutely  free  from  dust  is  also  free  from  bacteria,  and 
by  stirring  up  dust  the  number  of  germs  in  the  air  can  be 
increased  to  countless  multitudes. 

Germs  that  are  not  killed  by  drying  are  in  dust,  and  on 
being  inhaled  may  cause  disease.  As  long  as  people  con- 
tinue to  spit  on  the  streets  and  in  other  public  places,  the 
dust  about  cities  and  towns  will  contain  germs  of  consump- 
tion, catarrh,  and,  to  a  certain  extent,  of  diphtheria  and  pneu- 
monia. The  dust  in  houses  where  people  are  sick  of  these 
diseases  often  contains  the  germs,  and  it  is  quite  possible 
that  the  germs  of  whooping-cough,  measles,  mumps,  and  other 
contagious  diseases  which  we  do  not  well  understand,  may 
also  be  in  dust. 

People  should  be  prohibited  from  spitting  where  it  will  be 
a  danger  to  the  public,  but  every  possible  effort  should  also 
be  made  to  keep  down  dust.  Streets  should  be  cleansed  and 
sprinkled,  houses  should  be  swept  with  carpet  sweepers  or 
damp  brooms,  and  some  damp  material1  should  be  used  in 
sweeping  public  schoolrooms  and  other  public  buildings. 
Schoolrooms  should  be  swept  after  school  so  that  there 
will  be  time  for  the  dust  to  settle  before  the  pupils  assemble 
the  next  morning,  and  other  public  buildings  should  be 


1  The  Michigan  State  Board  of  Health  recommends  the  following  for  use  in 
sweeping  the  floors  of  public  buildings  : 

(1)  To  a  pailful  of  sawdust  wet  with  hot  or  cold  water,  add  one  half  pint  of 
kerosene  and  a  tablespoonful  of  sulpho-naphthol  or   formaldehyde.     This  ma- 
terial can  be  prepared  some  days  in  advance  of  its  use. 

(2)  Heat  one  third  part  sand,  and  add  two  thirds  part  sawdust.    To  a  pailful  of 
this  mixture  add  one  half  pint  of  paraffin  oil  and  mix  thoroughly.     This  prepa- 
ration produces  excellent  results. 

(3)  Boil  one  pound  of  salsoda  and  one  pound  of  chlorid  of  lime  in  a  gallon 
of  water.      Dampen  sawdust  to  be  used  for  sweeping  with  this  solution.     This 
preparation  is  excellent  for  restoring  the  natural  color  of  floors. 


PREVENTING    THE  SPREAD    OF  DISEASE  GERMS     327 

swept  some  time  before  they  are  to  be  used.  Dusting 
should  be  done  with  a  damp  cloth  that  will  wipe  off  the  dust 
and  take  it  away,  for  it  is  foolish  simply  to  stir  up  the  dust 
into  the  air,  where  it  will  be  inhaled  or  will  settle  again  on 
objects  in  the  room.  In  rooms  that  are  much  used,  hard 
floors,  rugs,  and  plain  furniture  are  more  hygienic  than  heavy 
carpets  and  plush-covered  furniture,  because  it  is  easier  to 
keep  them  free  from  dust.  Vacuum  cleaners  are  recom- 
mended by  health  officials,  because  they  remove  dust  and  do 
not  stir  it  up  where  it  will  be  breathed  into  the  lungs. 

DANGERS   FROM   WATER   AND    FOOD 

Typhoid,  dysentery,  and  diarrhoea  are  the  main  diseases 
that  are  carried  by  water.  All  over  our  country,  every  year, 
many  persons  contract  these  diseases  from  the  water,  and 
occasionally  the  water  supply  of  a  city  will  be  so  infected 
that  an  epidemic  will  occur.  The  way  water  may  be  pol- 
luted is  shown  by  the  history  of  the  typhoid  epidemic  from 
which  Butler,  Pennsylvania,  suffered  in  the  summer  and 
autumn  of  1903. 

Butler  was  then  a  city  of  about  16,000  inhabitants,  supplied 
with  water  from  an  artificial  lake.  A  family  living  on  the 
banks  of  a  small  stream  that  flowed  into  the  lake  was  stricken 
with  typhoid,  and  the  wastes  from  the  sufferers  were  thrown 
out  on  the  ground  near  the  creek.  The  germs  found  their 
way  into  the  creek,  and  into  the  water  that  was  used  in 
the  city,  and  soon  great  numbers  of  the  inhabitants  were 
stricken  with  typhoid,  about  1200  cases  developing  before  the 
epidemic  was  over.  One  section  of  the  city  was  supplied 
with  water  from  artesian  wells,  and  the  people  using  this 
water  did  not  suffer  from  the  disease,  which  shows  that  the 
germs  were  carried  by  the  polluted  water  from  the  lake. 


328  HUMAN  PHYSIOLOGY 

Epidemics  like  the  one  in  Butler  are,  of  course,  uncommon, 
but  if  you  will  investigate,  you  will  probably  find  that  in 
the  town  or  community  in  which  you  live,  several  persons 
die  each  year  from  these  water-borne  diseases. 

Freeing  Water  from  Disease  Germs.  By  filtering  through 
beds  of  sand,  a  city  can  take  almost  all  dangerous  germs  out 
of  its  water  supply.  Many  cities  fail  to  do  this,  however,  and 
when  one  must  use  impure  city  water  or  water  from  an 
ordinary  well,  the  best  plan  is  to  boil  it.  Bringing  it  to  a 
boil  will  kill  all  dangerous  germs,  most  of  them  dying  if  the 
water  is  heated  to  160  or  170  degrees.  Most  house  filters  are 
almost  useless,  for  they  catch  matter  in  which  the  bacteria 
breed  and  multiply,  and  the  bacteria  pass  through  the  pores 
in  most  of  them.  Filters  made  of  fine  porcelain  do  keep 
back  bacteria  if  they  are  carefully  cleaned  and  attended  to, 
but  this  is  a  great  deal  of  work,  and  it  is  easier  to  boil  water 
than  to  look  after  a  filter.  It  is  always  to  be  remembered 
that  to  wash  fruits,  vegetables,  dishes,  or  milk  vessels  in 
impure  water  may  be  as  dangerous  as  to  drink  the  water. 

Disease  Germs  in  Natural  Waters.  Any  water  that  comes 
from  the  surface  of  the  ground  is  likely  to  contain  disease 
germs,  typhoid  fever  being  a  very  common  disease  in 
the  country  and  in  mountainous  regions,  where  the  people 
drink  from  the  most  beautiful,  clear  springs.  Shallow  wells, 
springs,  and  small  streams  are  the  most  dangerous  of  all 
waters.  Cistern  water,  where  the  cistern  is  closely  cemented 
and  kept  clean,  is  much  safer.  Water  caught  from  a  roof 
and  stored  in  a  tank  above  ground  is  safe,  and  deep  arte- 
sian water  is  also  free  from  dangerous  germs.  It  is  never 
safe  to  use  water  from  a  shallow  well,  no  matter  how  cool 
and  clear  the  water  may  be,  for  experience  shows  that  people 
who  use  such  water  suffer  greatly  from  typhoid  fever  and 


PREVENTING   THE  SPREAD   OF  DISEASE   GERMS     329 

other  intestinal  diseases.  Some  wells  are  much  worse  than 
others,  an  occasional  well  giving  typhoid  to  almost  every 
family  that  uses  water  from  it.  Such  a  well  should  be  filled 
up,  and  if  water  from  a  suspicious  source  must  be  used  for 
drinking,  it  should  be  boiled. 

Keeping  Bacteria  out  of  Wells.     Very  few   bacteria   live 
deeper  than  three  or  four  feet1  in  the  soil.     The  pollution 


FIG.  156.  B  shows  how  surface  water  enters  a  well,  carrying  with  it  germs  from 
the  surface  of  the  soil.  A  is  a  well  arranged  to  keep  out  surface  water  and  germs. 
The  water  must  not  be  allowed  to  run  down  behind  the  wall,  the  platform  should  be 
double  and  water  tight,  and  water  should  not  be  allowed  to  run  back  into  the  well 
around  the  pump. 

of  wells  comes  from  surface  water  getting  into  them  when 
it  rains,  and  carrying  with  it  bacteria  from  the  upper  layers 
of  the  soil. 

To  keep  out  bacteria,  a  well  should  first  of  all  be  located 
on  a  high  place  and  away  from  all  pigpens,  stables,  or  out- 
buildings that  may  drain  into  it.  Around  the  mouth  of  the 

1  Where  the  soil  is  very  coarse  gravel  or  where  it  is  underlaid  by  sloping, 
cracked  layers  of  rock,  germs  may  travel  considerable  distances  underground. 


330  HUMAN  PHYSIOLOGY 

well  a  tough  clay  should  be  spread  and  packed  in  thoroughly, 
so  as  to  form  a  water-tight  layer  over  the  soil.  This  should 
slope  so  as  to  carry  all  surface  water  away  from  the  well. 
A  sound,  clean,  water-tight  platform,  large  enough  to  extend 
out  over  the  walls,  should  be  built,  so  that  no  surface  water 
whatever  will  run  in  behind  the  wall  and  get  into  the  well. 

The  whole  task  is  to  keep  the  surface  water  out  of  the 
well.  Cementing  the  upper  part  of  the  well  and  laying  a 
circle  of  cement  over  the  surface  of  the  earth  above  the 
mouth  of  the  well  is  the  surest  way  of  doing  this.  Where 
there  are  disease  germs  in  the  ground,  some  of  them  are 
likely  to  get  into  the  water,  but  their  number  can  be  greatly 
lessened  by  taking  proper  care  of  a  well.  Also  a  great  deal  of 
the  food  materials  on  which  the  germs  in  the  water  grow  and 
multiply  is  kept  out  of  the  well  by  these  precautions.  No 
one  who  is  nursing  a  case  of  infectious  disease  should  come 
about  the  well,  or  at  least  should  use  great  care  if  he  does 
so,  for  it  is  an  easy  matter,  by  handling  well-buckets  or  by 
working  around  a  pump,  to  leave  germs  where  they  will 
get  into  the  well. 

Dangers  from  Milk.  The  great  danger  from  milk  is  due 
to  the  fact  that  most  kinds  of  germs  multiply  rapidly  in  it. 
Tuberculosis  is  sometimes  caused  by  milk,  and  the  sickness 
that  is  so  common  among  young  children  in  summer  is 
often  due  to  germs  in  the  milk.  Typhoid  fever,  scarlet  fever, 
and  diphtheria  may  also  be  contracted  through  milk.  Again 
and  again  it  has  been  found  that  along  the  route  of  a  cer- 
tain milkman  the  people  were  suffering  from  one  of  these 
diseases,  and  on  investigation  it  would  be  proved  that  a  case 
of  the  disease  existed  among  those  handling  the  milk  or  in 
their  families ;  or  that  the  bottles  had  been  taken  back  from 
families  where  the  disease  was,  or,  in  epidemics  of  typhoid 


PREVENTING   THE  SPREAD   OF  DISEASE  GERMS    331 

fever,  that  the  milk  vessels  had  been  washed  in  water  from 
wells  containing  the  typhoid  germ.  One  article  in  a  medical 
iournal  reported  330  epidemics  traceable  to  milk,  of  which  195 
were  typhoid  epidemics,  99  were  epidemics  of  scarlet  fever, 
and  36  were  diphtheria  epidemics.  It  is  difficult  for  a  private 
citizen  to  guard  himself  against  these  dangers,  and  in  all  well- 
governed  cities  and  towns  a  health  officer  looks  after  the 
milk  supply. 

Keeping  Milk  Free  from  Germs.  All  milk  vessels  and  feed- 
ing bottles  for  babies  should  be  thoroughly  scalded  every  day 
to  kill  the  germs  in  the  milk  that  adheres  to  them.  Other- 
wise these  germs  will  multiply  in  the  new  milk,  and  soon 
it  will  be  filled  with  them  (page  303).  Milk  vessels  should 
never  be  rinsed  in  any  but  boiled  water,  the  purest  of  rain 
water,  or  artesian  water,  for  one  dangerous  germ  that  gets 
into  the  milk  from  the  water  remaining  on  the  vessels  may 
grow  into  a  multitude.  Milking  should  be  done  in  a  clean 
building  that  has  fly  screens  on  it,  and  everything  possible 
should  be  done  to  keep  dust  and  hairs  out  of  the  milk,  for 
these  are  swarming  with  germs.  The  milk  should  be  cooled 
as  quickly  as  possible,  and  kept  cool  to  prevent  the  germs 
from  multiplying  so  rapidly  (page  130).  It  should  be  used 
before  it  becomes  old,  for  milk  that  at  first  has  only  a  mod- 
erate number  of  germs  in  it  may  soon  be  filled  with  countless 
myriads  of  them.  It  is  also  necessary  for  a  medical  officer 
to  examine  the  cows  from  which  the  milk  comes,  or  there 
will  frequently  be  living  tuberculosis  germs  in  the  milk 
(page  341). 

Killing  Germs  in  Milk.  When  it  is  impossible  to  obtain 
clean  fresh  milk,  it  is  often  advisable  to  heat  milk  to  170 
degrees  or  a  little  higher  for  a  few  minutes,  or  to  heat  it  to 
155  degrees  for  half  an  hour.  This  destroys  most  of  the 


332  HUMAN-  PHYSIOLOGY 

germs  in  the  milk,  and  a  person  using  the  milk  has  fewer  of 
them  to  kill  out.  A  few  children,  however,  do  not  digest  the 
heated  milk  so  well  as  raw  milk,  and  heating  does  not  render 
wholesome  very  old  milk,  in  which  the  germs  already  have 
produced  large  quantities  of  toxins  and  acids.  In  the  sum- 
mer, however,  ordinary  milk  is  in  most  cases  greatly  im- 
proved by  heating. 

Dangers  from  Other  Foods.  Almost  any  food  may  be  a 
carrier  of  disease  if  it  has  been  exposed  to  flies  or  placed 
where  dust  may  blow  on  it.  The  intelligent  citizen  buys  his 
food  from  the  groceryman  who  keeps  a  clean  store  and 
screens  his  fruits  and  vegetables  from  flies. 

DISINFECTION 

It  cannot  be  too  strongly  emphasized  that  nearly  all 
our  germ  diseases  come  from  other  persons  who  are  diseased, 
and  that  insects,  dust,  water,  and  milk  are  sources  of  danger 
because  they  may  become  contaminated  with  germs  from  the 
body  of  some  person.  In  preventing  the  spread  of  germ  dis- 
eases, the  destruction  of  the  germs  in  sputum  and  in  the 
other  discharges  from  the  bodies  of  the  sick  is  therefore  more 
important  than  any  other  precaution.  It  is  well  for  every 
one  to  know  some  of  the  ways  of  killing  germs. 

Drying.  Many  germs,  especially  germs  like  the  typhoid 
and  cholera  germs,  die  if  they  are  thoroughly  dried.  No 
disease  germs  can  grow  and  multiply  when  dry,  and  suffi- 
cient drying  will  kill  almost  any  germ.  Yet  the  tuberculosis 
germ  can  stand  weeks  and  months  of  drying,  and  the  germ 
of  tetanus  may  be  dried  almost  indefinitely  without  killing  it. 
Therefore  it  is  usually  not  safe  to  depend  on  drying  alone 
to  disinfect  anything;  but  a  damp  house  keeps  alive  the 


PREVENTING    THE  SPREAD   OF  DISEASE   GERMS      333 

germs  that  are  in  it,  and  consumption,  pneumonia,  and  other 
diseases  are  more  likely  to  develop  in  a  damp  house  than  in 
a  dry  house. 

Light.  Light  is  injurious  to  bacteria,  bright  sunlight  kill- 
ing many  germs  in  a  few  hours,  and  a  moderately  strong 
light  assisting  in  checking  their  growth.  It  is  an  excellent 
practice  to  expose  bedclothes  and  rugs  to  the  sun,  and  to 
throw  up  the  shades  and  allow  the  light  to  enter  houses.  In 
rooms  occupied  by  consumptives,  or  by  pneumonia,  diph- 
theria, or  grip  patients,  this  is  especially  valuable.  Besides 
the  effect  which  light  itself  has  on  the  bacteria,  admitting  the 
light  dries  out  a  room,  and  assists  in  this  way  in  killing  the 
germs.  Dirt  and  dust,  mingled  with  sweat  and  oil  from 
the  skin,  on  doorknobs,  banisters,  and  furniture,  protect 
germs  from  light  and  drying,  thus  keeping  them  alive.  For 
this  reason  the  doorknobs  and  desks  in  schoolrooms  should 
be  cleaned  occasionally  with  soap  and  hot  water. 

Heat.  Boiling  water  kills  the  germs  of  all  common  dis- 
eases, and  handkerchiefs,  dishes,  and  clothing  that  have  be- 
come infected  can  be  made  safe  again  by  thoroughly  boiling 
them.  Articles  of  little  value,  and  sputum  from  patients 
sick  of  respiratory  diseases,  may  often  be  most  conveniently 
disposed  of  by  burning  (page  342).  The  surfaces  of  dishes 
contain  tiny  crevices  in  which  germs  lodge,  and  in  disin- 
fecting dishes  with  hot  water,  it  is  necessary  to  leave  them 
for  a  few  minutes  in  boiling  water,  so  that  the  heat  will  reach 
the  germs  in  the  crevices. 

Chemical  Disinfection.  Certain  chemicals  are  so  poison- 
ous to  germs  that  they  are  extensively  used  in  disinfecting. 
A  physician  should  always  be  consulted  as  to  which  disin- 
fectant is  best  for  a  particular  purpose,  and  exactly  how  to 
use  it,  for  some  of  them  are  better  for  one  purpose  than 


334  HUMAN  PHYSIOLOGY 

for  another.  Since  most  of  these  disinfectants  are  very  poi- 
sonous, an  excellent  plan  is  to  add  a  little  red  ink  or  other 
coloring  matter  to  them  so  that  they  will  not  be  mistaken 
for  water.  The  following  are  some  of  the  most  commonly 
used  disinfectants  : 

Bichlorid  of  mercury  (corrosive  sublimate)  dissolved  in 
water,  with  one  part  of  the  bichlorid  to  a  thousand  parts  of 
water  (i  dram  to  I  gallon  of  water),  kills  nearly  all  kinds  of 
germs  in  two  or  three  minutes,  and  all  kinds  in  fifteen  min- 
utes. This  can  be  purchased  in  tablets  of  the  right  size  to 
make  a  pint  or  half  pint  of  the  disinfectant  of  the  proper 
strength.  It  is  convenient,  and  an  excellent  disinfectant  for 
the  hands,  for  washing  floors  and  furniture,  and  for  disinfect- 
ing clothing  that  can  be  soaked  in  it.  It  cannot  be  used  on 
metal,  as  it  destroys  it,  and  is  not  good  for  disinfecting  where 
there  is  much  organic  matter  present,  as  there  is  in  dis- 
charges from  persons  sick  with  typhoid  and  other  intestinal 
diseases. 

Biniodid  of  mercury  is  more  than  twice  as  powerful  as 
bichlorid  of  mercury,  and  need  be  made  only  half  as  strong. 
It  is  one  of  the  best  general  disinfectants,  and  is  especially 
useful  in  disinfecting  the  hands,  since  it  does  not  injure  the 
skin  as  do  most  other  disinfectants. 

Carbolic  acid,  made  up  in  a  2^  per  cent  solution  (3-^  ounces 
of  liquid  carbolic  acid  to  I  gallon  of  water),  is  as  strong  as 
the  bichlorid  of  mercury  solution  described  above.  This  is  a 
very  reliable  disinfectant,  good  for  almost  any  purpose.  For 
disinfecting  sputum  and  other  discharges  from  the  body  it  is 
well  to  use  a  5  per  cent  solution. 

Lysol  is  about  the  same  strength  as  carbolic  acid.  It  often 
destroys  the  colors  in  clothing. 

Formalin  is  about  one  half  as  strong  as  carbolic  acid,  a  5 


PREVENTING   THE  SPREAD   OF  DISEASE  GERMS     335 

per  cent  solution  being  equal  to  a  I  to  1000  solution  of 
bichlorid  of  mercury.  It  loses  its  strength  if  exposed  to  the 
air.  By  heating  formalin,  a  gas  called  formaldehyde  is  driven 
off.  This  is  the  best  of  all  gaseous  disinfectants. 

Chlorid  of  lime,  made  by  adding  6  ounces  of  chlorid  of  lime 
to  i  gallon  of  water,  is  a  cheap  and  powerful  disinfectant. 

Milk  of  lime  is  a  powerful  disinfectant.  It  is  made  by 
adding  one  part  of  freshly  slaked  lime  by  weight  to  four 
parts  of  water.  This  is  a  cheap  disinfectant,  and,  for  certain 
purposes,  is  as  effective  as  anything  that  can  be  employed. 
It  should  not  be  used  in  sinks,  for  it  will  cause  trouble  with 
the  traps.  Air-slaked  lime  is  worthless. 

Special  Points  in  disinfecting.  Any  one  who  is  waiting  on  a 
person  sick  with  an  infectious  disease  should  frequently  and 
thoroughly  disinfect  his  hands,  holding  them  for  several 
minutes  in  the  disinfectant.  Washing  the  hands  thoroughly 
with  soap  assists  very  greatly  in  freeing  them  from  germs. 
Keeping  the  nails  trimmed  and  the  skin  smooth  makes  the 
hands  easier  to  disinfect. 

For  treating  an  infected  wound  or  a  sore,  peroxid  of  hydro- 
gen and  iodin  are  often  used.  A  weak  solution  of  carbolic 
acid  or  a  carbolic  salve  is  also  good,  and  washing  with  warm 
salt  water  is  useful  (page  312).  In  vaccination  the  skin 
should  be  cleansed,  clean  instruments  used,  and  the  wound 
protected  ;  for  the  greatly  swollen  arms  and  running  sores 
that  sometimes  follow  vaccination  are  caused  by  pus-forming 
germs  that  get  into  the  wound. 

In  typhoid  fever,  the  germs  are  in  the  discharges  from  the 
bowels  and  the  kidneys,  and  should  be  received  in  vessels 
containing  disinfectants.  Strong  limewater  is  excellent  for 
this,  and  carbolic  acid  is  also  good.  It  is  necessary  to  see 
that  the  disinfectant  is  thoroughly  mixed  with  the  waste 


336  HUMAN  PHYSIOLOGY 

matter,  and  it  should  be  allowed  to  stand  for  several  hours  to 
make  sure  that  all  germs  are  killed. 

In  diphtheria,  pneumonia,  consumption,  grip,  measles, 
scarlet  fever,  and  spinal  meningitis,  the  germs  are  in  the  dis- 
charges from  the  throat  and  nose.  It  is  best  to  receive  these 
discharges  -in  strong  disinfectants,  carbolic  acid  being  good 
for  this  purpose.  Above  all,  do  not  allow  the  discharges  to 
dry  and  become  scattered  about.  All  handkerchiefs,  dishes, 
and  other  infected  articles  should  be  placed  at  once  in  boiling 
water  or  soaked  in  carbolic  acid  or  bichlorid  of  mercury. 
These  substances  are  poisonous,  and  must  afterwards  be 
rinsed  off  dishes.  Additional  instructions  in  regard  to  the 
disinfection  of  sputum  will  be  found  in  the  chapter  on  con- 
sumption (page  342). 

Where  a  whole  room  or  house  is  to  be  disinfected,  it  is 
usually  done  by  fumigating.  Formaldehyde,  or  sometimes 
sulphur,  is  used  for  this  purpose.  Special  directions  are 
necessary  for  this  work  if  it  is  to  be  effectively  done.  Quick- 
lime is  a  good  disinfectant  for  cellars  and  closets,  and  the 
germs  in  any  matter  that  is  buried  in  quicklime  will  be 
killed. 

Mistaken  Ideas  in  Regard  to  Disinfection.  The  idea  that 
there  is  some  connection  between  the  smell  of  a  substance 
and  its  power  as  a  germ  killer  is  prevalent.  Odoriferous 
substances  are  sometimes  burned  in  rooms  containing  sick 
persons,  or  a  little  carbolic  acid  exposed  in  a  saucer  so  that 
it  will  scent  the  air  of  the  room.  It  need  hardly  be  pointed 
out  that  germs  are  not  injured  by  anything  of  this  kind. 

Unhygienic  Habits.  There  are  numerous  ways  by  which 
germs  can  get  into  the  body,  and  we  will  call  attention  to 
a  few  habits  which  give  them  a  special  opportunity  to  do 
so.  One  of  these  is  the  habit  of  putting  pencils  and  other 


PREVENTING   THE  SPREAD   OF  DISEASE  GERMS      337 

objects  into  the  mouth,  often  after  these  same  objects  have 
been  in  the  mouths  of  other  people.  Another  is  the  habit 
of  drinking  from  the  same  cup  that  others  use.  Germs  may 
easily  be  left  on  a  cup  by  any  one  who  has  them  in  his  mouth, 
and  each  child  in  school  should  have  his  own  cup,  and  in 
traveling  one  should  carry  a  private.cup.  When  it  is  neces- 
sary to  drink  from  a  public  cup,  it  is  better  to  put  both  lips 
into  the  cup  and  drink  without  taking  the  edge  of  the  cup 
into  the  mouth.  One  other  habit  that  we  would  mention  is 
that  of  allowing  the  fingers  to  touch  the  face,  eyes,  or  lips. 
In  many  ways  —  from  books,  doorknobs,  pencils,  seats  and 
straps  in  street  cars,  and  from  the  hands  of  other  persons  — 
we  get  germs  on  our  hands.  It  is,  therefore,  advisable  to 
form  the  habit  of  keeping  the  hands  away  from  the  face. 
Especial  attention  should  be  given  to  this  point  when  sore 
eyes  are  prevalent.  A  good  habit  to  form  is  that  of  washing 
the  hands  with  soap  before  eating  (page  335). 

Freeing  the  Country  Farmhouse  from  Disease.  By  intel- 
ligent effort,  families  living  in  the  country  can  greatly  de- 
crease the  risk  of  exposure  to  germs.  If  they  will  clear 
away  weeds  and  dense  shrubbery  from  around  their  homes 
and  look  after  the  breeding  places  of  mosquitoes,  they  can  do 
much  to  protect  themselves  against  malaria.  By  removing 
the  breeding  places  of  flies  and  guarding  their  own  milk  and 
water  supplies,  they  can  in  a  great  measure  free  themselves 
from  typhoid  fever.  Sunlight  admitted  to  the  house  is  a 
great  aid  in  keeping  the  atmosphere  free  from  germs,  and 
the  fresh  country  air  admitted  freely  to  the  sleeping  rooms 
at  night  will  do  much  to  build  up  the  body  and  increase  its 
germicidal  power.  Germ  diseases  are  almost  as  prevalent  in 
the  country  as  in  the  city,  but  with  a  little  care  a  family  in 
the  country  can,  to  a  great  extent,  avoid  them. 


338  HUMAN  PHYSIOLOGY 

City  and  Village  Improvement.  If  the  inhabitants  of  cities 
and  towns  will  work  together,  they  can  do  much  that  will  give 
them  more  healthful  and  also  more  pleasant  and  beautiful 
places  to  live.  Sprinkling  the  streets  and  sodding  with  grass 
along  the  sidewalks  will  help  to  keep  down  the  dust.  Clean 
sidewalks  are  pleasanter  than  sidewalks  that  are  covered 
with  sputum,  and  a  street  car  that  has  been  soiled  by  persons 
spitting  on  the  floor  is  neither  inviting  nor  sanitary.  By 
cutting  down  the  weeds  and  looking  after  the  breeding 
places  of  mosquitoes,  the  town  is  made  more  beautiful  and 
attractive  as  well  as  freed  from  malaria,  and  killing  out  the 
flies  saves  us  from  annoyance  as  well  as  from  disease.  The  in- 
telligent citizen  favors  the  improvement  of  his  town  because 
it  gives  him  a  more  pleasant  place  to  live,  and  because  he 
knows  that  it  costs  far  less  to  make  a  town  clean  and  health- 
ful than  to  have  all  the  disease  that  comes  from  insects, 
unclean  streets  and  sidewalks,  dust,  bad  water,  and  impure 
milk. 

The  Necessity  for  Public  Health  Officials.  There  are 
always  some  careless  persons  who  will  spread  disease  if 
they  are  permitted  to  do  so,  and  in  a  town  or  city,  it  is 
impossible  for  a  person  to  protect  himself  against  germ 
diseases  by  his  private  efforts.  He  has  no  control  of  his 
neighbor's  flies  and  mosquitoes,  and  he  cannot  prevent  con- 
sumptives from  scattering  germs  about  where  he  is  likely 
to  inhale  them.  If  he  lives  in  a  city,  he  has  no  water  ex- 
cept that  which  comes  to  him  through  the  city  water  mains, 
and  no  milk  supply  except  that  which  the  milkman  furnishes 
him.  His  children  may  go  to  school  and  there  be  kept  in 
an  unclean,  badly  ventilated  schoolroom,  and  seated  beside 
some  one  who  has  just  recovered  from  diphtheria,  and  who 
is  still  carrying  virulent  diphtheria  germs  in  his  throat.  With- 


PREVENTING   THE  SPREAD    OF  DISEASE  GERMS      339 

out  public  health  officers,  a  private  citizen  will  be  exposed 
in  a  hundred  ways  to  danger  from  disease  germs.  It  is, 
therefore,  the  duty  of  every  good  citizen  to  uphold  the 
health  officials  and  to  work  with  them,  and  every  one  should 
realize  that  it  is  a  great  moral  crime  to  scatter  abroad 
germs  that  may  cause  sickness  and  death. 

Summary.  Disease  germs  are  carried  by  insects,  dust, 
water,  and  food,  and  in  other  ways.  They  come  from  per- 
sons who  have  germ  diseases.  By  destroying  the  germs  that 
come  from  these  persons,  more  can  be  done  to  prevent  sick- 
ness than  in  any  other  way.  Country  people  may  protect 
themselves  against  germs,  but  in  cities  and  towns  health 
officials  are  necessary. 

QUESTIONS 

What  insects  carry  disease  germs  ?  What  diseases  are  carried  by 
mosquitoes?  Give  the  life  history  of  the  mosquito.  How  may  the 
malaria-carrying  mosquito  be  distinguished  from  other  mosquitoes? 
How  may  mosquitoes  be  destroyed?  How  do  flies  carry  germs? 
How  may  flies  be  destroyed  ?  Mention  some  measures  that  assist 
in  the  prevention  of  dust. 

Name  some  diseases  that  are  carried  by  water.  Tell  of  the 
Butler  typhoid  epidemic.  How  may  water  be  kept  safe  from 
germs?  What  natural  waters  contain  disease  germs?  What  kinds 
are  safe  ?  Tell  how  to  protect  a  well  from  germs.  What  diseases  are 
carried  by  milk?  What  measures  are  necessary  to  keep  milk  safe 
from  germs?  How  may  disease  germs  in  milk  be  killed?  What 
precautions  should  be  taken  to  keep  germs  from  foods? 

Name  four  ways  in  which  germs  may  be  killed.  Name  some 
common  chemical  disinfectants.  How  should  sputum  be  disposed 
of  ?  Mention  some  unhygienic  habits.  What  measures  will  assist 
in  freeing  a  farmhouse  from  disease?  in  freeing  cities  and  towns, 
from  disease?  Why  are  health  officials  necessary? 


CHAPTER   XXVI 


TUBERCULOSIS 

ABOUT  one  seventh  of  the  human  race  and  one  tenth  of  the 
inhabitants  of  the  United  States  die  of  tuberculosis.  Each 
year  this  disease  claims  in  Europe  about  one  million  vic- 
tims, and  in  our  own  country  about  one  hundred  and  fifty 
thousand.  This  means  that  each  day  four  hundred  of  our 
countrymen  die  of  tuberculosis,  and  that  eight  millions  of 
the  people  now  living  in  the  United  States  will  die  of  the  dis- 
ease. It  is  estimated  that  tuberculosis  costs  our  nation  in 
money  $330,000,000  a  year,  an  annual  sum  that,  if  properly 
expended,  would  free  the  land  from  the  disease. 

The  Bacillus  of  Tuberculosis.  Tuberculosis  is  caused  by  a 
slender  bacillus  that  attacks  most  vertebrate  animals  as  well 
as  man.  It  may  grow  in  almost  any  part  of 
the  body  and  cause  tuberculosis  of  the  part 
affected.  When  it  grows  in  the  intestine,  it 
causes  tuberculosis  of  the  intestine.  When  it 
grows  in  the  bone,  it  causes  tuberculosis  of 
the  bone.  When  it  grows  in  the  lymphatic 
glands,  it  causes  the  disease  formerly  known 
as  scrofula,  and  when  it  grows  in  the  lungs, 
it  causes  tuberculosis  of  the  lungs,  or  con- 
sumption. The  germ  of  tuberculosis  may  also  grow  in  the 
skin,  kidneys,  liver,  or  larynx,  but  it  most  frequently  attacks 
the  lungs. 

340 


FIG.  157.  The 
bacillus  of  tuber- 
culosis. 


TUBERCULOSIS  341 

The  bacillus  of  tuberculosis  is  slow-growing,  but  it  is  so 
hardy  that  it  often  resists  all  efforts  of  the  body  to  kill  it,  and 
grows  steadily  on  and  on  until  it  causes  death.  Outside  of 
the  bodies  of  men  and  animals,  it  does  not  grow  at  all  in 
nature,  and  under  the  influence  of  light  and  drying,  it  finally 
dies.  Yet  in  the  sputum  of  a  consumptive,  it  often  lives  for 
two  or  three  months  —  sometimes  for  one  or  two  years.  Dried 
sputum  blowing  about  in  dust  is  therefore  a  very  great  source 
of  danger  to  all  who  breathe  it  in.  Away  from  the  habitations 
of  men  and  animals,  the  tuberculosis  germ  is  not  found,  but 
it  is  frequently  present  in  the  dust  of  rooms  that  have  been 
occupied  by  careless  consumptives. 

HOW  TUBERCULOSIS   IS  CONTRACTED 

Tuberculosis  is  contracted  from  men  and  animals  that  have 
the  disease.  The  germ  gets  into  the  body  usually  either  from 
the  milk  of  diseased  cattle  or,  more  commonly,  from  the 
sputum  of  a  consumptive. 

Tuberculosis  Germs  in  Milk.  A  great  number  of  cattle  are 
affected  with  tuberculosis.  Occasionally  the  germs  are  in 
meat,  but  more  frequently  they  are  in  milk.1  It  is  known 
that  the  germs  of  tuberculosis  can  pass  through  the  wall  of 
the  alimentary  canal,  be  carried  by  the  blood  to  the  lungs, 
and  there  start  consumption.  Since  no  one  wants  to  drink 
living  tuberculosis  germs  in  his  milk,  dairy  cattle  should 
certainly  be  properly  inspected  to  see  that  they  are  free  from 
this  disease.  Yet  the  Alaska  Indians,  the  Filipinos,  and 
many  other  peoples  who  do  not  use  milk  suffer  greatly  from 

1  From  examinations  of  milk  made  in  Washington,  D.C.,  it  was  estimated 
that  almost  7  per  cent  of  the  milk  sold  in  the  city  contained  living  tuberculosis 
germs.  The  germs  are  also  found  in  butter  that  is  made  from  infected  milk,  and 
will  remain  alive  and  virulent  in  butter  for  weeks  and  months. 


342  HUMAN  PHYSIOLOGY 

tuberculosis,  and  it  is  probable  that  most  tuberculosis  comes 
not  from  milk,  but  from  persons  who  have  consumption. 

Dangers  from  Sputum.  In  the  advanced  stages  of  con- 
sumption, the  sputum  that  is  brought  up  from  the  lungs 
each  day  contains  several  billion  germs.  This  sputum 
should  never  be  swallowed,  for  if  this  is  done,  there  is  danger 
that  the  disease  will  be  started  in  the  walls  of  the  alimentary 
canal,  or  that  the  germs  will  get  into  the  blood  and  be  carried 
to  parts  of  the  body  that  have  not  yet  been  infected.  It  is 
also  unsafe  to  spit  the  sputum  out  where  it  will  be  exposed 
to  flies,  or  to  let  it. dry  and  blow  about,  for  it  may  cause 
other  people  to  contract  the  disease.  The  germs  in  the 
sputum  should  therefore  be  destroyed. 

Disposal  of  Sputum.  The  sputum  from  a  consumptive 
should  be  received  in  a  vessel  that  contains  a  disinfectant 
(carbolic  acid  or  chlorid  of  lime  is  good  for  this  purpose),  or 
in  pasteboard  cups  that  may  be  burned.  Sometimes  the 
sputum  is  received  in  vessels  that  contain  water,  and  is  then 
disinfected  with  boiling  water  or  buried  in  lime,  but  it  is 
safer  to  receive  it  in  a  disinfectant.  When  the  consumptive 
is  away  from  home,  he  may  use  pieces  of  cloth  and  seal  them 
up  in  waterproof  envelopes  that  are  made  for  the  purpose, 
until  they  can  be  destroyed. 

Other  Precautions  to  be  taken.  A  consumptive  should 
always  hold  a  handkerchief  before  his  face  when  he  coughs, 
and  these  handkerchiefs  should  be  placed  in  disinfectants,  or 
should  be  thoroughly  boiled.  He  should  learn  to  keep  his 
hands  away  from  his  face  and  mouth,  and  should  occasionally 
wash  his  hands  in  a  disinfectant.  He  should  have  his  own 
dishes,  and  these  should  never  be  washed  with  those  of  the 
family,  nor  allowed  to  come  in  contact  with  them  until  they 
have  been  boiled  for  at  least  five  minutes.  His  bedclothes, 


TUBERCULOSIS  343 

clothing,  and  furniture  ought  occasionally  to  be  disinfected, 
or  at  least  exposed  to  the  bright  sunshine  as  much  as  possible, 
and  his  clothing  should  be  boiled  before  it  is  washed  with 
other  clothes.  A  consumptive  should  have  a  sleeping  room 
to  himself,  and  this  room  should  be  kept  bright  and  well 
ventilated,  to  help  kill  any  germs  that  may  be  free  in  it. 
A  house  in  which  a  consumptive  has  lived  should  be  dis- 
infected before  any  one  else  moves  into  it. 

Danger  from  a  Consumptive.  If  care  be  taken,  a  consump- 
tive can  live  with  his  family  with  little  danger  to  them  ;  but 
if  he  is  careless  and  scatters  about  the  millions  of  germs 
that  come  from  his  lungs,  he  is  a  real  source  of  danger  to  all 
who  come  in  contact  with  him.  Many  persons  have  a  great 
fear  of  all  consumptives,  but  this  is  unreasonable,  for  it  is 
only  the  careless  consumptive  that  is  to  be  feared. 


THE  TREATMENT  OF   CONSUMPTION 

Probably  every  one  inhales  tuberculosis  germs  at  some 
time,  and  in  the  lungs  of  most  persons  there  are  scars  show- 
ing where  the  tubercle  bacilli  have  started  to  grow,  but  have 
been  destroyed.  It  is,  therefore,  a  great  mistake  to  think 
that  consumption  is  incurable. 

Importance  of  Early  Treatment.  Any  one  who  has  symp- 
toms of  consumption1  should  not  try  to  persuade  himself 
that  his  symptoms  have  no  existence,  for  this  will  not  stop 
the  growth  of  the  germs.  He  should  not  lose  valuable  time 
experimenting  with  patent  medicines,  for  there  is  no  medi- 

1  The  most  common  symptoms  of  consumption  are  cough,  loss  of  appetite, 
gradual  loss  of  flesh  and  strength,  fever,  night-sweats,  and  blood-spitting.  The 
cough  is  often  absent  in  the  early  stages  of  the  disease.  Only  an  examination  by 
a  reliable  physician  should  satisfy  one. 


344  HUMAN-  PHYSIOLOGY 

cine  known  that  will  cure  consumption.  The  only  sensible 
thing  for  him  to  do  is  to  be  examined  at  once  by  a  physician 
who  thoroughly  understands  the  disease.  Then,  if  he  finds 
that  the  germs  have  gained  a  foothold  in  his  lungs,  he  should 
give  himself  the  best  possible  treatment  at  once,  for  every- 
thing depends  on  starting  the  treatment  early. 

Important  Factors  in  Treatment.  In  the  successful  treatment 
of  consumption,  the  following  are  the  more  important  factors  : 

Rest.  If  a  consumptive  can  be  kept  quiet,  much  of  the 
toxin  that  is  produced  by  the  germs  will  be  thrown  off  in  the 
sputum.  Anything  that  causes  the  breathing  to  be  quick- 
ened and  deepened  causes  more  of  the  toxin  to  be  carried 
from  the  lungs  through  the  body,  and  increases  the  fever. 

A  consumptive  should  therefore  have  rest.  If  he  has 
fever,  he  should  have  absolute  rest,  not  even  walking  about 
his  room.  Laughing  and  loud  talking  should  be  avoided, 
and  coughing  should  be  refrained  from  as  much  as  possible. 
When  there  is  no  fever,  a  little  exercise  may  be  taken,  but  it 
should  be  taken  with  care. 

Food.  A  consumptive  should  have  an  abundance  of  food, 
especially  of  proteid  and  fatty  foods.  Meats,  eggs,  milk, 
and  any  other  good  foods  that  he  can  eat  and  digest  should 
be  taken.  Lunches  should  be  eaten  between  meals  and  on 
retiring.  The  foods  must  be  well  prepared  and  served  in 
different  ways,  or  the  patient  will  become  tired  of  them. 

Outdoor  Life.  Nothing  in  the  treatment  of  consumption  is 
more  important  than  fresh  air,  and  the  disease  has  been  most 
successfully  treated  where  the  patients  have  lived  and  slept 
in  the  open  air,  summer  and  winter.  Usually  an  upper  porch 
can  be  arranged  with  little  expense,  so  that  the  patient  can 
sleep  on  it.  In  outdoor  sleeping  in  winter,  it  is  necessary  to 
have  warm  clothing  and  to  wear  some  kind  of  hood  to  protect 


TUBERCULOSIS  345 

the  head  and  neck,  and  in  many  places  in  summer  it  is  neces- 
sary that  the  patient  be  screened  from  mosquitoes. 

OtJier  Important  Points.  Warm  and  dry  clothing  is  of 
course  important,  and  if  a  consumptive  lives  indoors,  he 
should,  above  all  else,  be  sure  to  have  plenty  of  fresh  air. 
Consumption  is  much  more  frequent  in  damp  houses  and  on 
wet  soils,  than  it  is  in  dry  houses  and  on  sandy  soils.  A  con- 
sumptive should  not  remain  in  a  damp  house,  and  if  he  lives 
outdoors,  he  should  locate  himself  on  a  dry  soil.  He  should 
not  worry  about  his  disease  being  inherited,  but  should  be 
cheerful  and  hopeful,1  for  if  he  takes  his  disease  in  time,  he 
has  every  reason  to  hope  for  recovery. 

Sanatoria  for  Consumptives.  Many  states  have  established 
sanatoria  to  which  consumptives  can  go,  and,  at  a  slight  ex- 
pense, remain  until  they  recover  from  the  disease.2  This  is 
sensible,  for  in  a  sanatorium  a  consumptive  can  have  proper 
food  and  care  at  much  less  expense  than  he  can  have  them 
at  home,  and  the  physicians  in  the  sanatorium  know  how  to 
disinfect  so  that  there  is  no  danger  of  the  spread  of  the 
disease.  It  is  much  more  economical  for  the  people  of  a 
state  to  care  for  their  consumptives  in  sanatoria  than  out  of 
them,  and  it  is  much  pleasanter  both  for  the  consumptives 
and  for  those  who  have  not  the  disease. 

.  l  When  consumption  carries  away  several  members  of  a  family,  the  trouble  is 
not  so  much  that  the  disease  is  inherited  (page  289),  as  that  the  members  of 
the  family  contract  the  disease  from  each  other.  It  has  been  found  that  persons 
who  have  married  consumptives,  or  who  have  lived  in  houses  that  were  infected 
with  the  germ,  contract  the  disease  almost  as  frequently  as  do  the  children  or 
the  brothers  and  sisters  of  consumptives. 

2  Many  state  and  city  boards  of  health  publish  circulars  giving  very  full  and 
detailed  information  in  regard  to  the  treatment  of  consumption.  A  consumptive 
should  write  to  the  health  board  of  his  state  for  these  circulars,  for  they  will 
enable  him  to  care  for  himself  much  more  intelligently. 


346  HUMAN"  PHYSIOLOGY 

The  Effect  of  Climate  on  Consumption.  It  .was  formerly 
supposed  that  climate  was  very  important  in  the  treatment 
of  consumption,  but  consumptives  are  now  being  cured  in 
all  our  states,  and  it  has  been  found  in  treating  this  disease, 
that  rest,  food,  and  fresh  air  are  of  much  more  importance 
than  climate.  Unless  a  consumptive  has  money  enough  to 
support  himself  without  work  and  to  give  himself  proper 
care,  he  should  not  leave  his  home  for  a  distant  state.  For 
in  many  places  consumptives  are  not  welcomed,  and  it  is 
better  to  be  at  home  and  have  the  proper  care  than  to  be 
without  money  or  friends  in  the  best  climate  in  the  world. 
A  hot  climate  or  a  high  elevation,  however,  is  injurious  to  con- 
sumptives, for  in  such  a  place  the  respiration  is  quickened. 

Summary.  Tuberculosis  costs  us  150,000  citizens  and 
$330,000,000  annually.  It  is  sometimes  contracted  from 
milk,  but  usually  from  the  sputum  of  consumptives.  Con- 
sumption readily  yields  to  treatment  when  taken  in  the  early 
stages.  Rest,  an  abundance  of  food,  and  fresh  air  are  the 
most  important  factors  in  the  successful  treatment  of  the 
disease. 

QUESTIONS 

Give  some  facts  that  show  the  importance  of  tuberculosis.  Tell 
something  about  the  bacillus  of  tuberculosis.  How  does  it  get  into 
the  body?  How  do  tuberculosis  germs  that  are  swallowed  in  milk 
get  to  the  lungs  ?  Why  is  there  reason  to  think  that  sputum  is  a 
more  common  cause  of  consumption  than  milk?  Why  should  sputum 
be  destroyed?  How  may  this  be  done?  What  other  precautions 
should  be  taken  in  consumption?  When  is  a  consumptive  to  be 
feared?  Give  three  important  factors  in  the  treatment  of  consump- 
tion. Mention  some  other  points  that  are  to  be  looked  after.  What 
advantages  come  from  having  sanatoria  for  consumptives?  How 
important  is  climate  in  the  treatment  of  consumption  ? 


APPENDIX 

A.    FOODS 

WHEN  the  foods  are  oxidized  in  the  cells,  and  when  a  piece  of 
wood  is  burned  in  the  fire,  the  process  is  the  same,  —  the  molecules 
are  broken  down,  and  their  atoms  are  united  with  oxygen.  What 
happens  to  the  foods  within  the  cells  may  perhaps  be  made  clearer, 
therefore,  by  considering  what  happens  in  the  burning  of  a  piece  of 
wood  or  coal  in  a  fire. 

The  Burning  of  a  Piece  of  Wood.  Lay  a  piece  of  wood  in  the  fire, 
and  in  a  little  while  the  wood  is  all  gone.  A  few  ashes  may  remain, 
but  these  are  only  a  little  mineral  matter  that  was  in  the  wood  and 
did  not  burn.  What  has  become  of  the  wood  ? 

The  answer  is  that  the  wood  has  been  changed  to  gases1  which 
you  cannot  see,  and  has  passed  off  into  the  air.  The  wood  mole- 
cules, like  starch  and  sugar  molecules,  are  built  up  of  atoms  of  car- 
bon, hydrogen,  and  oxygen.  In  the  fire  these  large  molecules  are 
broken  to  pieces,  and  the  atoms  in  them  unite  with  the  oxygen  of 
the  air.  The  carbon,  when  it  unites  with  oxygen,  forms  carbon 
dioxid.  The  hydrogen  of  the  wood  goes  off  in  water  vapor,  which 
is  invisible  when  it  is  hot.  By  holding  a  cold2  glass  vessel  over  a 
burning  piece  of  wood  or  over  a  burning  candle,  you  can  catch  and 
condense  on  the  inside  of  the  vessel  the  water  that  is  given  off. 
Of  what  elements  is  the  fat  of  a  candle  composed?  (Page  83.) 
Is  the  water  in  the  candle,  or  is  it  formed  when  the  fat  burns  ? 

1  Smoke  is  composed  of  fine  pieces  of  carbon  that  fly  off  into  the  air  with- 
out being  burned.     Only  a  very  small  part  of  wood  or  coal  passes  off  in  this  way. 

2  The    vessel  must  be  held  over  the  flame  only  a  very  short  time,  or  it  will 
become  so  hot  that  the  water  will  not  condense  on  the  glass.     A  tall  vessel  made 
of  heavy  glass  should  be  used. 

347 


348  APPENDIX 

Energy  set  Free  by  Oxidation.  Energy  is  stored  in  wood  molecules, 
and  in  the  fire  we  get  heat  and  light  from  these  molecules ;  energy  is 
stored  in  the  molecules  of  coal,  and  an  engine  gets  its  heat  and  its  power 
to  move  from  burning  coal ;  in  the  food  molecules,  too,  energy  is  stored, 
and  by  burning  these  molecules  the  cell  gets  its  heat  and  its  power  to 
work.  By  oxidation,  the  energy  in  the  molecules  is  set  free. 

Amount  of  Energy  needed  by  the  Body.  A  man  doing  light  work 
needs  daily  food  sufficient  to  furnish  2500  Calories^  If  he  does 
moderately  heavy  work,  he  needs  food  enough  to  furnish  3000 
Calories ;  and  if  he  does  heavy  work,  he  needs  food  enough  to  give 
3500  to  4000  Calories.  Many  hard-working  men  eat  food  sufficient 
to  give  5000  Calories,  and  some  lumbermen  working  in  the  Maine 
woods  in  the  cold  of  winter  were  found  to  be  eating  enough  food 
daily  to  furnish  8000  Calories  of  heat.  It  will  thus  be  seen  that  the 
amount  of  energy  the  body  needs  depends  very  largely  on  the 
amount  of  work  done,  and  on  whether  the  body  is  exposed  to  cold. 

Amount  of  Food  needed.  It  is  generally  supposed  that  from  one 
hundred  to  one  hundred  and  twenty-five  grams  (about  four  ounces)  of 
dry  proteid  matter  a  day  is  needed  to  keep  the  body  in  the  best  of 
health  (page  124).  In  nearly  every  community,  however,  there  is 
some  person  who  eats  chiefly  fruits,  nuts,  or  vegetables,  and  gets  far 
less  than  this  amount  of  proteid,  and  the  working  classes  of  the  Jap- 
anese live  on  about  forty-five  grams  of  proteid  a  day.  Also,  at  Yale 
University,  Professor  Chittenden  has  conducted  experiments  on 
teachers,  soldiers,  and  university  athletes.  For  five  months  these 
men  lived  on  from  forty  to  sixty  grams  of  proteid  matter  a  day,  — 
about  one  third  to  one  half  of  the  amount  generally  supposed  to  be 

1  A  Calorie  is  the  amount  of  heat  required  to  raise  the  temperature  of  one  liter 
of  water  i°  C.  Not  all  the  energy  of  the  foods  is  used  in  warming  the  body,  part 
of  it  being  used  in  building  protoplasm,  enzymes,  and  other  substances,  and 
part  of  it  by  the  muscles  in  doing  work.  But  the  easiest  way  of  measuring  the 
amount  of  energy  in  food  is  to  try  how  much  heat  it  will  give  oft"  when  it  is 
burned.  The  amount  of  energy  in  food,  therefore,  is  always  given  in  Calories, 
or  the  amount  of  heat  which  it  yields  when  burned. 


APPENDIX  349 

necessary  to  keep  a  man  in  health.  They  all  kept  in  good  health, 
and  most  of  them  gained  in  weight.  The  teachers  were  able  to  do 
good  mental  work,  and  some  of  them  thought  that  their  minds  were 
clearer  than  ever  before.  The  soldiers  attended  to  their  drills  and 
exercises  without  trouble.  The  athletes  gained  decidedly  in  strength  ; 
they  were  victors  in  many  contests,  and  one  of  them  won  the  Colle- 
giate and  All-around  Intercollegiate  Championship  of  America  in 
Athletics  while  living  on  this  small  amount  of  proteid.  It  therefore 
appears  that  some  persons  at  least  can  live  on  far  less  than  one  hun- 
dred grams  of  proteid  a  day.  In  the  opinion  of  most  physiologists, 
however,  it  is  better  for  most  of  us  to  take  a  larger  amount. 

Besides  the  necessary  amount  of  proteid,  we  must  have  food  to 
furnish  energy.  We  have  already  seen  that  the  amount  of  food  we 
need  for  this  purpose  varies,  and  that  it  is  best  to  take  for  energy 
foods,  carbohydrates  and  fats  (page  124).  The  exact  proportions  of 
the  fats  and  carbohydrates  are  not  important.  The  following  is  an 
old  diet  for  a  man  doing  moderate  work,  in  which  the  different  foods 
are  probably  in  about  the  right  proportions  :  — 

PROTEIDS  FATS  CARBOHYDRATES  CALORIES 

118  gms.          56  gms.  500  gms.  3°55 

QUESTIONS  AND   PROBLEMS 

i  gram  proteid  =  4.1  Calories.  i  kilogram  =  2.2  pounds. 

i  gram  proteid  carbohydrate  —  4.1  Calories.        i  pound  =  453.6  grams. 
i  gram  fat  —  9.3  Calories.  \  ounce  —  28.3  grams. 

To  walk  i  mile  on  the  level  requires  for  a  man  of  average  weight  (154 
pounds}  energy  equal  to  59  Calories. 

To  ascend  100  feet  (as  in  climbing  a  hill  or  a  flight  of  steps)  requires 
energy  equal  to  15.4  Calories. 

Which  is  the  cheaper  food,  cabbage  or  candy?  tomatoes  or  peanuts? 
bananas  or  raisins  ? 

How  far  could  a  man  walk  on  the  energy  in  10  cents'  worth  of  sirloin 
steak?  on  the  energy  in  10  cents'  worth  of  rice?  on  the  energy  in  10 
cents'  worth  of  sugar  ? 


350 


APPENDIX 


NAME  OF  FOOD 

§g 

w  s 

g£ 

PH 

INEDIBLE 
PORTION 

EDIBLE  PORTION 

PER  CENT  OF  AVAILABLE 
PROTEIDFAT  AND  CAR- 
BOHYDRATE IN  FOOD 
AS  PURCHASED 

| 

$ 

Unavailable 
nutrients 

Available  nutrients 

! 

£ 

Carbo- 
hydrates 

ri 

rs 

2 

1! 

f 

°7 
/o 

% 

% 

% 

% 

%. 

% 

% 

'% 

% 

Apples      .     .     . 

!-5 

25 

84.6 

1.6 

•3 

•5 

12.8 

.2 

.225 

•375 

9.6 

Bananas  .     .     . 

7 

35 

75-3 

2-7 

i 

•5 

19.9 

.6 

•65 

•325 

12.9 

Beans  (dried)    . 

5 

12.6 

7-5 

15.8 

1.6 

59-9 

2.6 

15.8 

1.6 

59-9 

Beef  (round)     . 

14 

7-2 

65-5 

1.6 

19.7 

12.9 

.8 

18.2 

11.9 

Beef1  .     .     .     . 

25 

13-3 

60.6 

1.8 

17.9 

19.2 

— 

.8 

J5-5 

16.6 

— 

Bread  (white)    . 

5 

35-3 

3-3 

7-i 

1.2 

52-3 

.8 

7-i 

1.2 

52-3 

Bread  (graham) 

5 

— 

35-7 

3-4 

6.9 

1.6 

5J-3 

i.i 

6.9 

1.6 

5J-3 

Breakfast  food2 

7-5 

— 

9.6 

4-5 

9-3 

1.6 

74 

i 

9-3 

1.6 

74 

Butter       .     .     . 

25 

— 

ii 

4-9 

i 

80.8 

2-3 

i 

80.8 

Cabbage  .     .     . 

2-5 

!5 

9i-5 

•7 

1.2 

•3 

5-5 

.8 

i 

•25 

4-675 

Candy      .     .     . 

20 

4 



95 

i 

— 

95 

Cheese      .     .     . 

16 

— 

34-2 

3-4 

25.1 

32 

2.4 

2-9 

25.1 

32 

2.4 

Corn  meal    .     . 

2 

— 

12.5 

4 

7-5 

J-7 

73-5 

.8 

7-5 

*.-7 

73-5 

Corn  (canned)  . 

5 

— 

76.1 

i-7 

2.1 

i.i 

18.3 

•7 

2.1 

i.i 

18.3 

^ggs  (boiled)     . 

14 

II.  2 

73-2 

1.2 

12.8 

11.4 

.6 

"•3 

10 

Filberts    .     .     . 

20 

52 

3-7 

10.7 

13-3 

58.8 

11.7 

1.8 

6-3 

28.2 

5-6 

Fish3  .     .     .     . 

IO 

54-8 

76.7 

I 

2O 

1.6 

•9 

9 

.72 

Fish  (salt  cod)  . 

7 

24.9 

53-5 

6.8 

20.9 

•3 

— 

18.5 

J5-7 

.22 

— 

Fowl  *  .... 

15 

25-9 

63-7 

1.6 

I8.7 

J5-5 

— 

.8 

13-8 

11.48 

— 

Liver   .... 

15 

7 

71.2 

1.2 

2O-4 

4-3 

i-7 

1.2 

18.97 

4 

1.58 

Milk  (whole)     . 

3 

87 

•5 

3-2 

3-8 

5 

•5 

3-2 

3-8 

5 

Milk  (skimmed) 

i 

1  — 

9°-5 

•3 

3-3 

•3 

5-1 

•5 

3-3 

•3 

5-1 

Mutton  (loin)    . 

20 

16 

50.2 

2.4 

J5-5 

3J-4 

.6 

*3 

26.3 

Oatmeal  (dry)  . 

4 

— 

7.8 

5-6 

13-4 

6.6 

65.2 

1.4 

i3-4 

6.6 

65.2 

Oysters  (solid)  . 

30 

— 

88.3 

.6 

5-8 

1.2 

3-3 

.8 

5-8 

1.2 

3-3 

Peanuts    .     .     . 

IO 

25 

9.2 

10.7 

21.9 

34-7 

22 

i-S 

16.4 

26 

16.5 

Peas  (green) 

7 

45 

74-6 

2.2 

5-2 

•5 

I6.7 

.8 

2.86 

•275 

9.18 

Pork  (fresh  loin) 

12 

19.7 

S-2 

2.2 

16.1 

28.6 

.8 

!2.9 

22.96 

— 

Pork  (salt  ham) 

2O 

13.6 

40.3 

3-6 

15.8 

36-9 



3-6 

13-6 

31.88 

— 

Potatoes  (white) 

!-5 

20 

78-3 

i-4 

i-7 

.1 

17.7 

.8 

1.36 

.08 

14.16 

Potatoes  (sweet) 

2 

20 

69 

2.1 

J-3 

.6 

26.2 

.8 

1.04 

48 

20.9 

Prunes  (dried)  . 

IO 

15 

22.3 

8-3 

1.6 

— 

66.1 

T-7 

1.36 

56-1 

Raisins  (dried)  . 

IO 

10 

14.6 

9.1 

2 

3 

68.7 

2.6 

1.8 

2-7 

61.8 

Rice     .... 

8 

— 

12.3 

3-7 

6-5 

•3 

76.9 

•3 

6-5 

•3 

76.9 

Strawberries 

7 

5 

90.4 

i 

.8 

•5 

6.8 

•5 

.76 

•475 

6.46 

Sugar  .... 

6 

— 

— 

IOO 

100 

Tomatoes      .     . 

i 

— 

94-3 

•4 

•7 

•4 

3-8 

•4 

•7 

•4 

3-8 

Watermelon  .     . 

i 

60 

92.4 

•9 

•3 

.2 

6 

.2 

.12 

.08 

2.4 

(tenderloin.) 


(wheat.) 


3  (black  bass,  whole.)  *  (chicken,  feathers  removed.) 


APPENDIX 


351 


FUEL  VALUES 

OF  FOOD   AS 

PURCHASED 

COST  OF 
PROTEID 

COST  OF  TOO  CAL- 
ORIES OF  HEAT 

AMOUNT  FOR  TEN  CENTS 

Ounces 

Grams 

Number  of 
Calories 

^ 

*a 

8. 

M  £ 

£5 

4 

§| 
«» 

3 

^ 

£ 

it 

31 

1 
1 

£ 

II 

62 

Cals. 

Cals. 

Dols. 

Dols. 

f 

!98 

43 

6.66| 

i-47 

•75 

•24 

•4 

IO.2 

6.8 

n-3 

290.3 

1320 

265 

58 

10.76 

2-37 

2.64 

.14 

.07 

2-9 

4.2 

2.1 

83.6 

378 

J475 

325 

•31 

.068 

•34 

5-°5 

•51 

19.16 

143-3 

14-5 

543-4 

2950 

840 

185 

.76 

.16 

1.6 

2.1 

1.36 



58-9 

38.5 

600 

989 

218 

1.61 

•35 

2-5 

•99 

i.  06 



28.1 

3O.I 

— 

395 

JI55 

254 

.70 

•!5 

•43 

2.27 

•38 

I6.7 

64.4 

10.88 

474-4 

2310 

1150 

253 

.72 

•i5 

•43 

2.26 

•5 

16.4 

62.6 

14-5 

465-4 

2300 

1617 

356 

.80 

•!7 

.46 

1.98 

•34 

J5-7 

56.2 

9.6 

447-5 

2156 

3427 

755 

25 

5-51 

.72 

.06 

5-1 

1.8 

146.6 

J37i 

116 

25 

2.50 

•55 

2.1 

.64 

.16 

2-99 

18.1 

4-5 

84.8 

464 

1767 

389 

I.I 

— 

— 

7.6 

— 

215.4 

883 

1861 

410 

.64 

.14 

.86 

2-5 

3-2 

.24 

71.1 

90.7 

6.8 

1163 

1578 

347 

.26 

.058 

•13 

6 

1.36 

58.8 

170 

38-5 

1667 

7890 

426 

94 

2.38 

•52 

i.i 

.67 

•35 

5-85 

19.05 

9-97 

166 

852 

632 

139 

1.24 

•27 

2.2 

1.29 

1.14 

36 

32-4 

— 

45  1 

1411 

311 

3-i7 

.69 

1.4 

•5 

2.25 

•44 

14.28 

63-9 

12.7 

705 

198 

43 

i.  ii 

.24 

5 

i-44 

.11 

— 

40.8 

3-26 

— 

198 

302 

66 

•44 

.098 

2-3 

3-58 

.04 

— 

101.7 

1.42 

— 

43i 

74i 

163 

1.09 

.24 

2 

1.47 

1.22 

— 

41.7 

34-7 

— 

494 

551 

121 

•79 

•J7 

2.7 

2 

.42 

.16 

57-3 

12 

4-77 

367 

312 

68.9 

•93 

.205 

.96 

I.7I 

2 

2.67 

48.4 

57-4 

75-6 

1040 

169 

37-2 

•3° 

.066 

•59 

5-3 

.48 

8.16 

149-7 

13.6 

231 

1690 

I351 

298 

J-53 

•33 

1.4 

1.04 

2.1 

— 

29.4 

59-6 

676 

1740 

383 

.298 

.065 

•23 

5-36 

2.64 

26 

JS1^ 

74-8 

739-3 

435° 

220 

48 

5-i7 

1.14 

13.6 

•3 

.06 

•J7 

8.76 

1.81 

4-98 

73 

1710 

376 

.60 

•13 

•59 

2.62 

4.l6 

2.64 

74-3 

117.9 

74-8 

1710 

235 

5i 

2-44 

•53 

2.9 

•65 

.06 

2.09 

18.5 

1.78 

59-4 

336 

1208 

266 

•93 

.20 

•99 

1.72 

3.06 

48.7 

86.7 

1006 

1598 

352 

i-47 

•32 

1.25 

i.  08 

2-55 

— 

30.8 

72.3 

— 

799 

292 

64 

I.IO 

.24 

•5i 

i-45 

.08 

J5-1 

41.1 

2.41 

428.1 

1947 

428 

94 

1.92 

.42 

.46 

•83 

•38 

16.72 

23-5 

10.88 

474- 

2140 

1070 

235 

7-35 

1.62 

•93 

.21 

8.97 

6.16 

— 

254-4 

1070 

1296 

285 

5-55 

1.  2O 

•77 

.28 

•43 

9.88 

8.16 

12.2 

280.3 

1296 

i564 

344 

1-23 

•27 

•5i 

!-3 

.06 

15-38 

36.8 

i-7 

436. 

X955 

J54 

33 

9.21 

2.03 

4-54 

•J7 

.1 

1.47 

4.92 

3-°7 

41.86 

220 

1860 

410 

•32 

— 

26.66 

— 

756 

3100 

100 

22 

1.42 

•31 

i 

1.  12 

.64 

6.08 

3J-75 

18.14 

!72-3 

1000 

50 

II 

8-33 

1.83 

2 

•19 

.12 

3-84 

5-44 

3.62 

108.8 

500 

352  APPENDIX 

A  man  is  too  fleshy  and  wishes  to  reduce  his  weight.  Suppose  that  he 
eats  just  enough  to  support  his  body  without  exercise.  How  far  must  he 
walk  to  take  off  five  pounds  of  fat? 

An  eight-year-old  boy  needs  about  half  as  much  food  as  a  man.  What 
would  be  a  fair  amount  of  carbohydrate  for  a  boy  of  this  age?  If  an  eight- 
year-old  boy  bought  half  a  pound  of  candy  and  ate  it  all  in  one  day,  in 
addition  to  his  usual  food,  how  much  carbohydrate  would  he  get  that  day  ? 

Suppose  that  in  walking  you  use  the  same  energy  in  proportion  to  your 
weight  as  does  the  average  man.  How  much  energy  will  you  use  in  walk- 
ing a  mile? 

How  much  energy  would  you  use  in  climbing  to  the  top  of  the  tallest 
building  that  you  know  ? 

How  much  energy  would  be  required  to  bring  you  from  your  home  to 
your  place  in  the  schoolroom  ? 

How  much  would  it  cost  to  buy  enough  bread  to  carry  you  ten  miles  ? 
enough  filberts  ?  enough  strawberries  ? 

How  much  potatoes  would  a  man  need  to  eat  to  get  100  grams  of  proteid? 

How  much  beef  would  he  need  to  eat  to  get  3000  Calories  of  energy  ? 
How  much  proteid  would  this  give  him? 

A  man  had  for  breakfast  two  eggs  (4  oz.),  two  slices  of  bacon  Q  oz.), 
3  slices  of  bread  (4  oz.),  butter  (|  oz.),  and  coffee  with  milk  (i  oz.)  and 
sugar  (|  oz.).  How  much  proteid,  fat,  carbohydrate,  and  energy  did  he 
get? 

How  much  money  would  be  required  to  buy  in  fresh  fish  the  amount  of 
proteid  that  can  be  bought  for  10  cents  in  corn  meal?  the  amount  of 
energy  that  can  be  bought  for  10  cents  in  oatmeal? 

If  a  man  eats  100  grams  of  proteid  and  100  grams  of  fat  a  day,  how 
much  carbohydrate  will  he  need  to  give  him  3500  Calories  of  heat  ? 

If  in  the  diet  on  page  349  the  carbohydrates  are  decreased  100  grams, 
how  much  must  the  fats  be  increased  to  give  the  same  amount  of  energy? 

Make  up  a  diet  offish,  bread,  eggs,  and  cheese  that  will  give  a  man  100 
grams  of  proteid.  How  much  fat  will  this  diet  give  him  ?  how  much  carbo- 
hydrates ?  how  much  energv  ?  What  would  be  the  objection  to  this  diet  ? 

Select  three  foods  from  the  list  on  page  350,  and  from  them  make  a  diet 
that  will  give  a  hard-working  man  the  proper  amounts  of  the  different 
classes  of  foods  and  of  energy. 

Weigh  your  own  food  for  a  day  and  calculate  how  much  of  the  different 
classes  of  foods  and  how  much  energy  you  get. 


APPENDIX  353 


B.    INTESTINAL  DISEASES 

The  long  intestinal  tract  affords  a  favorable  place  for  the  growth  of 
parasites,  and  the  parasites  find  an  easy  mode  of  entrance  to  this 
tract  in  the  food  and  water  that  are  taken  in  through  the  mouth. 
Children,  especially,  suffer  from  intestinal  diseases,  and  because  these 
diseases  cause  so  much  sickness  and  so  many  deaths,  it  is  important 
that  their  cause  and  the  means  of  prevention  be  understood. 

Diarrhoea.  Diarrhoea  may  be  caused  by  several  different  bacteria, 
all  of  which  grow  in  the  intestine,  and  most  of  which  are  closely 
related  to  the  typhoid  germ.  One  of  these  germs  causes  the  very 
severe  form  of  diarrhoea  that  runs  in  epidemics,  and  is  sometimes 
called  flux.  Poisoning  from  meats,  fish,  old  milk,  and  ice  cream  is 
due  to  germs  related  to  the  diarrhoea  bacteria.  The  germs  grow  in 
the  food  either  before  or  after  it  is  eaten,  and  produce  the  toxins 
that  cause  the  poisoning. 

Infant  Diarrhoea.  Summer  complaint,  from  which  so  many  young 
children  die,  is  caused  by  germs  belonging  to  this  same  group*  The 
disease  may  easily  be  started  in  a  little  baby  by  giving  it  impure 
water,  and  nothing  but  boiled  water,  pure  rain  water,  or  artesian 
water  should  ever  be  given  to  a  little  child  or  put  into  its  milk. 
Nearly  all  milk  contains  germs  that,  when  taken  in  large  enough 
numbers,  will  cause  the  trouble,  and  the  milk  supply  is  mainly  respon- 
sible for  the  disease.  The  disease  is  worse  in  summer  because  in 
warm  weather  the  germs  multiply  more  rapidly  in  milk,  and  also 
because  the  heat  weakens  the  children  so  that  they  have  not  much 
power  of  killing  germs. 

How  the  Germs  of  Intestinal  Diseases  are  Spread.  The  germs 
of  diarrhoea,  dysentery  (page  296),  and  typhoid  fever  are  usually 
swallowed  either  in  food  or  water.  They  are  carried  about  and 
get  into  the  food  and  water  in  various  ways  (page  315),  but  one 
especially  important  precaution  in  the  prevention  of  all  these  dis- 
eases is  to  keep  discharges  from  the  intestines  away  from  flies. 


354  APPENDIX 

Hookworms.  The  hookworm  is  a  slender  white  worm,  not  quite 
half  an  inch  in  length.  It  grows  in  the  intestines,  and  causes  a  pro- 
found anaemia  (lack  of  red  blood  corpuscles).  Hookworms  are  found 
in  the  warmer  parts  of  all  the  continents ;  they  cause  the  death  of 
one  third  of  the  people  of  Porto  Rico,  and  it  is  estimated  that  in 
our  own  country  south  of  the  Potomac  River  from  20  to  25  per 
cent  of  the  poorer  white  people  suffer  from  hookworms. 

How  Hookworms  get  into  the  Body.  The  eggs  of  the  hookworm 
pass  out  of  the  body  in  the  excreta  from  the  alimentary  canal.  If 
they  are  allowed  to  get  into  the  soil,  they  develop  into  worms  so  small 
that  there  may  be  fifty  of  them  in  a  piece  of  earth  the  size  of  a  pea. 
These  worms  may  enter  the  body  through  the  skin  (in  which  they 
cause  "  ground  itch  ")  and  be  carried  in  the  blood  to  the  intestine, 
or  they  may  be  taken  into  the  alimentary  canal  in  water  or  in  food. 
The  disease  is  more  common  among  children  than  among  adults, 
because  children  go  barefooted,  and  sometimes  eat  with  unwashed 
hands  after  playing  in  the  earth ;  it  is  more  common  among  agricul- 
tural laborers  and  brickmakers  than  among  those  who  do  not  come 
in  contact  with  the  soil ;  and  the  disease  is  more  severe  (though  not 
more  common)  in  the  white  than  in  the  colored  race. 

The  Prevention  of  Hookworm  Disease.  The  eggs  of  the  hookworm 
get  into  the  soil  only  from  persons  who  have  the  disease.  Away 
from  the  air  the  eggs  die,  and  the  disease  may  be  entirely  prevented 
by  the  use  of  water-closets.  In  hookworm  regions  great  care,  there- 
fore, should  be  exercised  to  prevent  the  pollution  of  the  soil  about 
houses.  To  a  certain  extent,  children  may  be  saved  from  infection 
by  the  wearing  of  shoes,  but  keeping  the  soil  free  from  pollution 
is  the  important  measure  in  the  prevention  of  hookworm  disease.1 

1  Often  it  is  not  realized  that  hookworm  victims  are  diseased,  and  they  are 
considered  lazy  and  ambitionless.  Many  cases  of  hookworm  trouble  are 
mistaken  for  malaria.  The  symptoms  of  hookworm  disease  are  paleness,  thin- 
ness, dull  skin  and  eyes,  dry  hair,  continued  weakness,  and  sometimes  an  appetite 
for  such  substances  as  earth,  tobacco  ashes,  and  paper.  The  worms  may 
readily  be  killed  and  the  disease  cured  by  the  use  of  very  simple  medicines. 


GLOSSARY 


This  glossary  is  intended  chiefly  to  help  the  pupil  in  the  pronunciation  of  the  more 
difficult  terms.  Words  are  defined  only  where  no  exact  definition  is  found  in  the  text. 
The  numbers  refer  to  the  pages  on  which  definitions  are  found. 


afferent  (af  fe-rent),  carrying  to. 

amoeba  (am-e'ba),  296. 

amylopsin  (a-mM6p'sin),  98. 

Anopheles  (an-6fel-ez),  321. 

aorta  (a-or'ta),  141. 

aqueous  (a'kwe-us),  watery. 

arachnoid  (a-rak'noid),  like  a  cob- 
web ;  as,  arachnoid  membrane. 

arbor  vitae  (ar'bor  vT'te),  215. 

arytenoid  (a-rl-te'noid),  173. 

bacillus  (ba-sfl'lus),  304. 

bacteria  (bak-te're-a),  285. 

biceps  (bi'seps),  67. 

bronchial  (bron'ke-al),  166. 

canine  (ka-nin'),  95. 

capillary  (cap'il-la-re),  141. 

carbohydrate  (kar-bo-hl'drat),  82. 

cartilage  (kar'til-aj),  gristle. 

cerebellum  (ser-e-beTliim),  25. 

cerebro-spinal  (ser'e-bro-spi'nal),  26. 

cerebrum  (ser'e-brum),  25. 

choroid  (ko'roid),  261. 

cilia  (sll'e-a),  plural  of  cilium ; 
minute,  hair -like  projections. 

coccus  (kok'us),  304. 

coccyx  (kok'six),  34. 

cochlea  (kok'le-a),  254. 

corpuscle  (kor'pusl),  a  cell  of  the 
blood  or  lymph  (page  147),  or  a 


group  of  cells,  as  a  renal  corpuscle 

(pagei88). 
cricoid  (kri'koid),  172. 
Culex  (kyu'iex),  321. 
cytoplasm  (si'to-plazm),  4,  footnote, 
dentine  (den'tin),  94. 
diaphragm  (di'a-fram),  17. 
dietetics  (dl-e-tet'iks),  the  science  or 

study  of  the  regulation  of  the  diet. 
diphtheria  (dif-the're-a),  304. 
dura  mater  (du'ra  ma'ter),  26. 
efferent  (ef  fe-rent),  carrying  from. 
enzyme  (en'zfrn),  112. 
epiglottis  (ep-r-glot'tis),  165. 
esophagus  (e-sofa-gus),  90. 
Eustachian  (yu-stak'e-an),  253. 
fasciculus  (fas-slk'yu-lus),  a  bundle. 
femur  (fe'mer),  37. 
fibula  (fib'yu-la),  37. 
formaldehyde  (for-mal'de-hld),  335. 
fungus  (fun'gus),  plural  fungi  (fun'- 

ji)»  3i8. 

hemoglobin  (hem-6-glo'bin),  148. 
hepatic  (^-^.M'^C),  pertaining  to  the 

livery  as,  hepatic  vein. 
hydrogen  (hi'dro-jen),  80. 
incisor  (in-si'sor),  95. 
infundibulurn.      (in-fun-dtb'yu-lum)^ 

166. 


355 


356 


GLOSSARY 


invertase  (in-ver'tas),  113,  footnote 

lachrymal  (lak'ri-mal),  pertaining  /< 
the  tears ;  as,  lachrymal  duct. 

lacteal  (lak'te-al),  152. 

larynx  (lar'inks),  165. 

lymph  (llmf),  149. 

lymphatic  (lim-fat'ik). 

malleus  (mal'le-us),  253. 

medulla    oblongata    (med-uTla    ob- 
lon-gah'ta),  25. 

Meibomian  (mi-bo'mi-an),  260. 

membrane  (mem'bran),  a  thin  layer 
of  tissue. 

meningitis  (men-in-ji'tis),  308. 

molecule  (mol'e-kyul),  79. 

mucus  (myu'kus),  168. 

neuron  (new'ron),  211. 

nitrogen  (ni'tro-jen),  80. 

nucleus  (new'kle-us),  4. 

olfactory  (ol-fak'to-re),  pertaining  to 
the  sense  of  smell. 

pancreas  (pan'kre-as),  98. 

papilla  (pa-pil'la),  193. 

parotid  (pa-rot'id),  97. 

patella  (pa-tel'la),  37. 

peptone  (pep'ton),  112. 

perimysium  (per-e-mlz'e-um),  62. 

periosteum  (per-e-6s'te-um),  42. 

phalanges  (fa-lan'jez),  37. 

pharynx  (far'inks),  90. 

pia  mater  (pi'a  ma'ter),  26. 

process    (pr6'sess),  a   slender,  pro- 
jecting point. 

proteids  (pro'te-ids),  83. 

protoplasm  (pro'to-plazm ) ,  the  living 
substance  of  the  cell. 

protozoon  (prp-to-zo'on),  plural  pro- 
tozoa (pro-to-zo'a),  285. 


psoas  (so'as),  70. 

ptyalin  (tl'a-lin),  98. 

pulmonary  (pul'mo-na-re),  having  to 
do  with  the  lungs. 

pylorus  (pl-16'rus),  93. 

rabies  (ra'be-ez),  299. 

renal  (re'nal),  pertaining  to  the  kid- 
neys ;  as,  renal  corpuscle. 

retina  (ret'i-na),  261. 

sacrum  (sa'krum),  34. 

salivary  (sal'i-va-re),  89. 

scapula  (skap'yu-la),  36. 

sclerotic  (skle-rot'ik),  261. 

sebaceous  (se-ba'shus),  195. 

spirillum  (spT-ril'lum),  304. 

stapes  (sta'pez),  253. 

steapsin  (ste-ap'sin),  98. 

subcutaneous  (sub-kyu-ta/ne-us),  193. 

submaxillary  (sub-maks'il-la-re),  97. 

tetanus  (tet'a-nus),  313. 

thoracic  (tho-ras'ik),  connected  with 
the  chest,  from  thorax,  chest. 

thyroid  (thl'roid),  172. 

trachea   (tra'ke-a),  the  windpipe. 

trapezius  (trap-e'ze-us),  60. 

triceps  (tri'seps),  67. 

trichina  (tri-kT'na),  129. 

trichinosis  (trtk-T-no'sis),  129. 

trypsin  (trip'sin),  98. 

tuberculosis  (tu-ber-kyu-lo'sis),  340. 

tympanic   (tTm-pan'ik),  252. 

tympanum  (tfm'pan-um),  253. 

urea  (yu're-a),  116. 

ureter  (yu-re'ter),  188. 

uvula  (yu'vyu-la),  165. 

vena      cava     (ve'na  ka'va),    plural 

venae  cavae  (ve'ne  ka/ve),  142. 
vitreous  (vlt're-us),  like  glass. 


INDEX 


A  star  (*)  after  a  page  number  indicates  that  an  illustration  of  the  subject  ap- 
pears on  that  page. 


Abdominal  cavity,  16,*  17;  muscles, 
60,*  70.* 

Absorption,  93,   110-119. 

Accidents,  274-283. 

Acid,  in  gastric  juices,  91,*  92,  113, 
113;  uric,  114,  116;  poison,  280. 

Afferent  nerves,  211,  217,  218,*  225,* 
226,*  245,  246,*  248. 

Air,  80,  178,  180,  229,  344.  See  also 
Oxygen  and  Carbon  Dioxid. 

Air  sacs,  161,  162,*  166,  167.* 

Alcohol  as  a  food,  131;  baths,  199 
(n.  i);  how  formed,  238;  and 
length  of  life,  239;  and  tuberculosis, 
240;  and  insanity,  241;  and  germ 
diseases,  290. 

Alcohol,  effects  of,  on  the  human  body, 
238-244;  muscles,  74,  233;  diges- 
tive organs,  101,  102,  116;  heart,  155; 
arteries,  155;  respiratory  system, 
171;  kidneys,  189;  nervous  system, 
232*;  animals,  233,  234,*  241;  char- 
acter, 243;  eyes,  271. 

Alimentary  canal,  88;  disease  germs 
in,  287,  315,  353. 

Amylopsin,  98,  113. 

Anatomy,  defined,  13. 

Animal  kingdom,   17,  19.* 

Animals,  composed  of  cells,  4,  5,  n; 
one-celled,  5,  6,*  7,  150. 

Antitoxins,  287  (n.  2),  306,  307. 

Aorta,  138,*  141,  143,*  186.* 

Appendix,  vermiform,  88,*  94,  94  (n.  2). 

Aqueous  humor,  261.* 

Arachnoid  membrane,  26. 

Arbor  vitse  ("tree  of  life"),  213,*  215. 


Arteries,  pulmonary,  138,*  141,  143*; 
hepatic,  138*;  aorta,  138,*  141; 
denned,  141;  circulation  in,  140, 
142*;  bleeding  from,  277,*  278.* 

Arytenoid  cartilages,  172,*  173,  174.* 

Atoms,  79-81. 

Auditory  canal.     See  Hearing. 

Auricles,  137,*  140,  141,  143.* 

Bacilli,  304.*     See  also  Bacteria. 
Bacteria,  diseases  caused  by,  303-318; 

in  foods,    130,  315,  327,  330,   353; 

defined,    285;    shapes  of,   304*;    of 

various  diseases,   305,*  308,*  310,* 

311,*  313,*  315,*  316,*  317,*  340.* 
Baths,  200-203. 

Bile,  duct,  90*;   in  the  liver,  99. 
Bladder,  gall,  88,*  90,*  99;    of  kidneys, 

186,*  189. 

Bleeding,' 27 7,*  278.* 
Blood,  cells  of,  7,  10,*  147*  (see   also 

Corpuscles);  circulation  of,  135-157; 

function    of,    135. 
Blood  vessels,   17,    26,    27,*    42,    91,* 


93, 


136,    138,*     141,     143,*     143, 


146,*    161,   162,*    191,*    195,*  198. 

Body,  human,  a  colony  of  cells,  3-15, 
135;  plan  of,  16-22;  cavities  of,  16,* 
17;  controlled  by  nervous  system, 
28,  210;  carriage  of,  53,  69-72;  laws 
governing,  135 ;  wastes  of,  see  Wastes; 
heat  of,  135,  191,  194,  197-199, 
202;  effects  of  alcohol  on,  238-244; 
equilibrium  of,  255. 

Bone,  cells  of,  7,  8,*  56;  materials  in, 
39,  40*;  marrow,  40,*  42,  147. 


357 


358 


INDEX 


Bones,  of  the  skeleton,  31-43,  32,* 
33>*  34,*  35»*  5°*>  52*;  broken,  55. 

Brain,  8,*  17,*  23,  24,*  25,*  48,  210, 
210  (n.  i),  213,*  265. 

Bright's  Disease,  alcohol  and,   189. 

Bronchial  tubes,  166,  167.* 

Burns,  treatment  of,  279. 

Calorie,  348,  348  (n.  i). 

Capillaries,  138,*  141,  142,*  144  (n.  i), 
148,*  150,*  151.* 

Carbohydrates,  82,  83,  124-128,  349. 

Carbon  dioxid,  81,*  148,  150,*  160, 
179,  180  (n.  i). 

Cartilage,  35,*  38,*  42,*  47,*  50; 
thyroid,  172*;  cricoid,  172*;  aryte- 
noid,  87,*  172,*  173,  174.* 

Cat,  brain  of,  229*;  eyes  of,  262.* 

Cell,  the,  3-15;    division  of,  5,*  6.* 

Cells,  human  body  a  colony  of,  3-15; 
kinds  of,  7,*  8,*  10,  89,*  56,  59 
(n.  i),  61,  91,*  188,  191,*  193,  200; 
ciliated,  9,*  147  (n.  i);  growth  of,  78, 
84;  energy  in,  78,  84,  114;  wastes  of, 
115,*  149,  150*;  foods  of,  7,  78,  79, 
114,  115,*  150*;  poison  in,  186,  287. 

Cerebellum,  25,*  213,*  215,  229.* 

Cerebro-spinal  fluid,  264  meningitis,  26 
(n.  i),  317  * 

Cerebrum,  25,*  213,*  214,*  229.* 

Chemistry  of  foods,  79,  80,*  81,*  82. 

Chest  (thoracic)  cavity,  16,*  17,  162.* 

Chills,  199,  202,  203,  293. 

Cholera,  316.* 

Choroid  coat  of  the  eye,  261,*  262,  266. 

Cigarettes.     See  Tobacco. 

Cilia,  6,*  9,*  147  (n.  i),  168. 

Ciliary  muscles,  266.* 

Circulation  of  the  blood,  135-159; 
diagram  of,  138*;  organs  of,  136- 
146,  139,*  142,*  143,*  146.* 

Clavicle  (collar  bone),  32,*  35,*  36. 

Cleanliness,  130,  200-202. 

Climate  and  tuberculosis,  346. 


Clothing,  170,  204,  205,  279. 

Cocci  (sing,  coccus),  304.* 

Coccyx,  34.* 

Cochlea,  254.* 

Colds,  203,  310. 

Compounds,  79-81. 

Connective  tissue,  8,*  n,  25,  27,*  42, 
47,*  62,*  63,*  89,*  91,*  143,  191.* 

Consumption.     See  Tuberculosis. 

Contraction,  of  muscles,  61,  65,  66*;  of 
auricles  and  ventricles,  137,  140; 
governed  by  the  cerebellum,  215. 

Convolutions  of  the  brain,  25,*  214. 

Cooking,  123,  128. 

Cornea,  261,*  266.* 

Corpuscles,  red,  7,  10,*  42,  85,  147,* 
148,  293*;  white,  10,*  147,*  153, 
288*;  renal,  187,*  188*;  touch  (tac- 
tile), 191,*  246,*  247. 

Cranial  nerves,  225. 

Cranium,  25,  26,*  34,  48. 

Cricoid  cartilage,  172.* 

Cytoplasm,  4  (n.  2). 

Dermis,  191,*  193,  195.* 

Diaphragm,  16,*  17,*  18,*  162  (n.  i), 
163,*  164  (n.  i). 

Diarrhoea,  353. 

Dietetics,  120-133. 

Digestion,  7,  9,  110-119,  121-123; 
organs  of,  88-109,  88>*  9°*5  alco- 
hol and,  101,  116;  juices  in,  91,  93. 
100;  hygiene  of,  120-123. 

Diphtheria,  304-307,  305*. 

Disease  germs,  285-290;  and  lymph 
nodes,  153,  154;  denned,  285;  alco- 
hol and,  290;  in  water,  315,*  324, 
327-329;  in  milk,  316  (n.  i),  330. 
See  also  Bacteria,  Protozoa,  etc. 

Diseases,  intestinal,  353~354- 

Disinfection,  312,  332-338. 

Dorsal  cavity,  16.* 

Drowning  accidents,  274,*  275,*  276.* 

Ducts.    See  Salivary,  Thoracic,  etc. 


INDEX 


359 


Dura  mater,  26. 

Dust,  170,  271,  325-327. 

Dysentery,  296.* 

Ear,  bones  of,  34,  253*;  divisions  of, 
252,*  253,  254*;  care  of,  255. 

Ear  drum  (tympanum),  253. 

Efferent  nerves,  211,  218,*  219,*  226.* 

Elements,  79-81. 

Energy,  foods  and,  78-87,  114,  124, 
349;  in  the  cells,  78,  84,  114;  oxida- 
tion and,  114,  160,  348. 

Enzymes  (ferments),  112,  113. 

Epidermis,  191,*  192,*  195.* 

Epiglottis,  165,  166,*  173.* 

Epithelium,  249,  249  (n.  i). 

Erector  spinae,  70,*  71.* 

Erysipelas,  311.* 

Esophagus,  17,*  88,*  90,  166.* 

Eustachian  tube,  252,*  253. 

Exercise,  12,  73,  123,  154,  170. 

Eyes,  259-273;  and  digestion,  123; 
effects  of  tobacco  on,  271-272; 
foreign  bodies  in,  278. 

Fainting,  278. 

Fat,  8,*  10,  42,  115,  191.* 

Fats,  as  food,  83,  113,  124,  153. 

Ferments  (enzymes),  112,  113. 

Fever,  198,  293. 

Fibers.     See  Nerve,  Muscle,  etc. 

Flies,  dangers  from,  324,*  325.* 

Follicle,  hair,  194,  195,*  200  (n.  i). 

Foods,  for  the  cell,  7,  78,  79,  114, 
115,*  150*;  and  energy,  78-87, 
114,  124,  349;  chemistry  of,  79-82; 
classes  of,  82-84;  digestion  of, 
110-119,  121-123;  oxidation  of, 
114,  160,  348;  amount  and  kinds 
needed,  124-128,  348;  alcohol  and, 
131-132;  for  consumptives,  344; 
table  of,  350-351. 

Foot,  48,*  49,  146.* 

Fungi,  287  (n.  i),  318.* 


Gall  bladder,  88,*  90. 

Ganglia,  210,  226,  227,*  228.* 

Gastric  glands  and  juice,  91,*  92. 

Germicidal  substance,  288,  290. 

Germs.     See  Disease  Germs,  Bacteria. 

Glands,  stomach,  7,*  25,  25  (n.  i),  91*; 
salivary,  25  (n.  i),  89,  97,*  98*; 
pancreas,  25  (n.  i),  98;  liver,  25 
(n.  i),  99;  kidney,  25  (n.  i);  sweat, 
25  (n.  i),  89  (n.  i),  191,*  193,*  194; 
simple,  89*;  secretions  of,  89, 
89  (n.  i);  cells  of,  7,*  89,*  91*;  gas- 
tric, 91*;  intestinal,  93*;  sublingual, 
97*;  submaxillary,  97*;  parotid, 
97*;  sebaceous,  195;  lachrymal, 
259,  260*;  Meibomian,  260. 

Grape  sugar,  112,  113. 

Gray  matter  (nerve  cells),  214,  217, 
229. 

Hair,  194,  195,*  196. 

Hand,  n,  37,  64,*  65.* 

Health  officials,  importance  of,  338. 

Hearing,  251-256;  organ  of,  252,* 
253,*  254  * 

Heart,  location  of,  17,*  18,*  137,  139*; 
function  of,  137;  auricles,  137*; 
ventricles,  137*;  valves  of,  140,* 
141*;  nerves  of,  145;  hygiene  of, 
154-156;  alcohol  and,  155;  tobacco 
and,  156;  and  the  great  blood 
vessels,  141,  142,  143.* 

Heat.     See  Body  Heat,  Heating. 

Heating  and  ventilation,  182,  197, 
202. 

Hemispheres  of  the  cerebrum,  214. 

Hemoglobin,  148. 

Hepatic,    vein   and   artery,    138,*  145. 

Heredity,  and  alcohol,  241;  and  tuber- 
culosis, 240,  345,  345  (n.  i). 

Hookworms,  354. 

Hydrophobia.     See  Rabies. 

Hygiene,  defined,  13;  of  the  skeleton, 
53-56;  muscles,  73-74;  digestive 


3  6o 


INDEX 


organs,  120-123;  heart,  154-156; 
respiratory  system,  170-172;  nervous 
system,  229-235. 

Impulses,  nerve,  211,  216,  217,  245. 
Incus  (anvil),  253.* 
Influenza  (Grip),  309,  310.* 
Insects,  as  disease  carriers,    287,   320- 

325>  32I>*  322>*  324>*  325-* 
Intestinal  diseases,  315,*  316,*  353. 
Intestine,    17,*    18*;     large,    88,*    94; 

small,  88,*  93,*  113,  152. 
Involuntary  muscles,  25,  61  (n.  i),  62. 
Iris,  261,*  262,*  266.* 
Iron,  80*;   in  the  blood,  85. 

Joints,  45,  46,  48*;  muscles  and,  61. 
Juices,  digestive,  91-93,  98,  100,  112. 

Kidneys,  7,  17,*  25  (n.  i),  186,*  187*; 

and    the     body    wastes,     186-190; 

alcohol  and,  189. 
Knee-cap.     See  Patella. 

Lachrymal,    bone,    33*;    glands,   259, 

260* 

Lacteals,  151,*  152  (n.  i). 
Larynx,  165,   166,*  167,*   172*,   173.* 
Lens,  of  the  eye,  261,*  263,  264,*  266.* 
Ligaments,  47,  48,*  55;    and  tendons, 

64,*  65*;   suspensory,  263,  266.* 
Light,  and  the  sense  of  sight,  262-267, 

270;   and  disease  germs,  333. 
Liver,  n,  17,*  18,*  25  (n.  i),  88,*  89; 

and   alcohol,    102,    116;    circulation 

in,  138,*  145  (n.  T). 
Lumbar  region,  69. 
Lungs,  7,  9,  n,  17,*  18,*  148  (n.  i), 

161,  163,*  167*;  circulation  in,  138,* 

162*;    air  sacs  in,    161,   162,*   166, 

167*;    in    drowning  accidents,   274. 
Lymph,    149,    150,*    151    (n.    i),    194; 

nodes,  139,*  152,*  153*;  and  disease 

germs,  154,  154  (n.  i). 


Lymphatic,  system,  151-154;  vessels, 
139,*  151,*  152  (n.  i). 

Malaria,  292-296;  germ  of,  293,* 
295  (n.  i);  mosquitoes  and,  294- 
296,  321,*  322,*  323. 

Malleus  (hammer),  253.* 

Malt  sugar,  in,  113- 

Mammals,  18,  19.* 

Man,   in  animal  kingdom,  17,  18,  19.* 

Medicines,  patent,  12,  130,  343. 

Medulla,   25,*   213,*    216,   229.* 

Meibomian  glands,  260. 

Membranes,  of  brain  and  cord,  25, 
26;  mucous,  90,  91,*  151,*  168. 

Meninges,  26  (n.  i);  disease  of,  317. 

Milk,  germs  in,  330-332,  341. 

Mind,  the  seat  of,  25,  210  (n.  i),  214. 

Mineral  matter,  in  bone,  39;  foods,  85. 

Molecules,  79,  80,*  81,*  no,  in,  114. 

Mosquitoes  and  malaria,  294-296, 
321,*  322,*  323. 

Motor  nerves.       See  Efferent. 

Mucous  membrane,  90,  91,*  151,*  168. 

Mucus,   9,*  90,  94,   1 68. 

Muscle,  cells,  7,  8,*  10,  61  (n.  i),  62,* 
150,*  2ii*;  tissue,  10,  59  (n.  i); 
fibers,  143. 

Muscles,  the,  59-77,  60*;  voluntary, 
23-25,  61  (n.  i),  68,  215;  involun- 
tary, 25,  61  (n.  i),  62;  contraction  of, 
61,  65,  66,*  215;  antagonistic,  67; 
of  head,  69*;  of  spinal  column, 
69,  70,*  71,*  72;  effects  of  alcohol 
and  tobacco  on,  74;  of  stomach,  92; 
of  the  hair,  195,*  195  (n.  i);  of  the 
eye,  260*;  ciliary,  266.* 

Nails,  the,  196. 

Nasal,  bone,  33*;  passages,  164,  166,* 
1 68;  cavity,  260.* 

Nerves,  cells  (gray  matter),  8,*  210; 
tissue,  10,  210;  of  brain,  10,  26, 
210  (n.  i),  214,  229;  fibers,  27,*  192,* 


INDEX 


361 


210,  211,*  219*;  function  of,  27;  in 
bone,  42;  of  the  heart,  145;  of  the 
skin,  191,*  192*;  cranial,  225; 
of  touch,  246,*  247;  of  taste,  249*; 
optic,  260,*  261,*  265.  See  also 
Afferent  and  Efferent. 

Nervous  system,  23-30,  210-237; 
central,  23,  213-224;  sympathetic, 
23,  226-228;  like  a  telegraph  sys- 
tem, 28;  and  the  muscles,  68;  and 
the  sweat  glands,  194;  like  a  tele- 
phone system,  212*;  of  other  ani- 
mals, 229*;  hygiene  of,  229-235; 
tobacco  and  alcohol  and,  230-235. 

Neurons,  211,*  218. 

Nitrogen,  80,  84. 

Nodes.     See  Lymph. 

Nucleus,  of  cells,  4,  61  (n.  i),  211*; 
division  of,  5,*  6.* 

Olfactory  organs.     See  Smell. 

Optic  nerve,  260,*  261,*  265. 

Organs  of  the  body,  n,  17,*  18,*  23. 

Oxidation  of  foods,  114-115,  i6o,*348. 

Oxygen,  and  the  cells,  7,  9,  114,  148, 
148  (n.  i),  161;  carried  by  red  cor- 
puscles, 7,  148,  148  (n.  i);  in  air, 
178,  179.  See  also  Oxidation. 

Pancreas,  17,*  25  (n.  i),  88,*  89,  90,* 

98,  113;  juices  of,  98,  113. 
Papillae,   191,*  192,*  193,    195.* 
Pasteur  treatment,  300. 
Patella  (knee-cap),  32,*  37,  60.* 
Pelvis,  bones  of,  32,*  35,*  36. 
Pepsin,  89  (n.  i),  92. 
Peptones,  112. 

Pericardium,  163,*  163  (n.  i). 
Periosteum,  40,*  42,*  63,  64. 
Pharynx  (throat),  90,  164,  166.* 
Physiology,  defined,  13. 
Pia  mater,  26. 
Plasma,  146,  147,  149. 
Pleura,  161,  162,*  163.* 


Pneumonia,     308,      309;       germ     of, 

308* 

Poisoning,  treatment  for,  280-281. 
Poisons,  in  cells,  120,  121  (n.  i),  186, 

287;    in  air,    178,    179. 
Pons,  213,*  216. 

Portal  circulation,  138,*  145  (n.  i). 
Processes,   bone,    38*;     spinous,   38*; 

vocal,  172.* 

Proteids,  83,  113,    124,   125,   153,  348. 
Protoplasm,  4,   n,   12,   13,  61   (n.   i), 

78,  84. 

Protozoa,  285,  292-302. 
Ptyalin,  98,  112. 
Pulmonary,   artery,    138,*    141,    143*; 

veins,  138,*  142. 
Pupil  of  the  eye,  261,*  262.* 
Pylorus,  90,*  93,  113. 

Quarantine,  306. 
Quinine,  256,  295,  296. 

Rabies  (Hydrophobia),  299-300. 

Reflex,  centers,  217,  219;  actions, 
217,  218,*  219,*  220,  221,  227. 

Renal,  artery,  186*;  vein,  186*;  cor- 
puscles, 187,*  188.* 

Respiration,  160-177;  organs  of,  161, 
162,*  163,*  164,  165,  166,*  167,  168; 
artificial,  274,*  275,*  276.* 

Rest,  12,  73,  271,  344. 

Retina,  261,*  265,*  267,*  269. 

Ribs,  32,*  35,*  36. 

Sacrum,  34,*  35.* 

Salivary  glands,  25  (n.  i),  89,  97,*  98.* 

Scapula,  32,*  35,*  36,  38.* 

Sclerotic  coat  of  the  eye,  261,*  266. 

Sebaceous  glandfc,  195.* 

Semicircular  canals,  254,*  255. 

Sensations,  215,  245. 

Senses,  the  special,  245-273. 

Sensory  nerves.     See  Afferent  Nerves. 

Shoulder  blade.     See  Scapula, 


362 


INDEX 


Skeleton,   the,    31-58,    32*;    principal 

bones   of,    33,*   34,*   35,*    3^,    37; 

effect  of  tobacco  on,  56. 
Skin,  the,   8,*    191,*  192,*  195,   246*; 

and  the  body  heat,  191-208. 
Skull,  32  *  33  * 
Sleep,  183-184,  229-230. 
Smallpox,  297,*  298. 
Smell,  the  sense  of,  250,*  251. 
Spinal  column,   16,*  17,  31,  32,*  34,* 

49,  54,  69,  71. 
Spinal  cord,  16,  17,*  24,*  25,  26,*  28, 

217,  219,  225,*  226,*  227,*  228.* 
Spinous  processes,  38,*  70. 
Spirilla,  304.* 
Spleen,  17,*  18,*  88,*  138.* 
Sputum,  305,  308,  326,  342. 
Stapes  (stirrup),  253.* 
Starch, £2,  in,  113,  116. 
Steapsin,  98,  113. 
Sternum  (breast  bone),  32,*  35.* 
Stimuli,  nerve  (impulses),  211,  216. 
Stomach,  7,*    9,     17,*  18,*  88,*  90,* 

91,*  92,*   138*;    function  of,  91;  of 

various  animals,  105.* 
Subcutaneous  layer,  191,*  193. 
Sugar,  a  carbohydrate,    82;    digestion 

of,  in,  113,  145  (n.  i);    malt,  in, 

113;    grape,  112,  113;  and  villi,  153. 
Suspensory  ligament,  263,  266.* 
Sweat  glands,  25  (n.  i),  89  (n.  i),  191,* 

193,*  194,  198,  227. 
Sympathetic   nervous  system,    23,   62, 

226-228,  227.* 

Tactile    (touch)  corpuscles,   246,*  247. 
Tapeworm,  129,*  129  (n.  i). 
Taste,  246,  249.* 
Teeth,  89,  94,  95,*  96,*  103. 
Temperature.  See  Body  Heat,  Heating. 
Tendons,  63,*  64.* 
Tetanus  (lockjaw),  313,*  314. 
Thoracic  (chest)  cavity,  16,*  17,  162*; 
duct,  152,  153. 


Thyroid  cartilage,  172.* 
Tissues,    10,    59  (n.  i),    210. 
Tobacco,   effects  of,  on    the   skeleton, 

56;     muscles,   74;     heart,    156-157; 

respiratory    system,     172;     nervous 

system,  230-232;    eyes,  271-272. 
Tongue,   97,*     104.* 
Tonsils,  165. 

Touch,  191,*  246,*  247,*  248.* 
Toxins,  287,  293. 

Trachea,  9,*  17,*  161,  163,*  165,  166.* 
Trichina,  129.* 
Trypsin,  98,  113. 
Tuberculosis,  240,  340*^46 . 
Tympanic  membrane,  252,*  253.* 
Tympanum  (ear  drum),  253. 
Typhoid  fever,  286,  315,*  316  (n.  i), 

324,  327,  328. 

Urea,  116,  186,  187;  alcohol  and,  116. 
Ureter,  186,*  187,*  188. 
Uric  acid,  114,  116,  186,  187. 
Uvula  (soft  palate),  165,  166.* 

Vaccination,  297-299. 

Valves  of  the  heart,  137,*  140,*  141.* 

Veins,    89,*    138,*    141,    142,*    143,* 

186*;   bleeding  from,  277. 
Venae  cavae,    137,*    138,*    142,*    143.* 
Ventilation,  178-185,  182,*  183.* 
Ventral  cavity,  16,*  17. 
Ventricles,  137,*  140,  143.* 
Vertebrae,  34,*  38.* 
Vertebrates,  18,  19,*  20,  5o*~53. 
Villi,  93,*  94  (n.  i),  151,*  152. 
Vitreous  humor,  261.* 
Vocal  cords,  165,  172,*  173,*  174,*  175. 
Voluntary  muscles,  23,  61,  62,  215. 

Wastes,  7,  17,  114,  115,*  136,  149,  150.* 

Water,  81,*  187,  191,  191  (n.  i);    and 

disease  germs,  286,  315,  327-330. 

Yeast,  238.* 


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